A Strategy to Design High-Density Nanoscale Devices utilizing Vapor Deposition of Metal Halide Perovskite Materials

Sustainable Mixed-Halide Perovskite Resistive Switching Memories Using Self-Assembled Monolayers as the Bottom Contact

The complex ionic-electronic conduction in mixed halide perovskites enables their use beyond von Neumann architectures implemented in resistive switching memory devices. Although device fabrication based on perovskite compounds involves solution-processing at low temperatures, reducing further fabrication costs by eliminating expensive materials can improve their compatibility with upscalable deposition techniques. Notably, the substrate on which the perovskite active layer is developed has been reported to severely affect its quality and thus the overall device performance. Hereby, we demonstrate the sustainable manufacturing of memristive perovskite solar cells by replacing the expensive poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) that serves as a hole transporting layer (HTL) with a self-assembled monolayer (SAM), namely [2-(3,6-dimethoxy-9H-carbazol-9-yl)ethyl]phosphonic acid (MeO-2PACz). Multiple sequential memristive current-voltage characteristics of single devices are reported, and average data of multiple reference and targeted devices are compared. Resistive switching memory devices based on SAM exhibit improved performance having reduced average SET voltage values and narrower statistical variation compared to reference devices with PTAA. It is shown that both PTAA and SAM based devices exhibit high ON/OFF ratio of about 103 operating at low switching electric fields. Replacing an expensive polymer-based HTL with this approach reduces fabrication costs compared to PTAA.

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.

Thermally Evaporated Metal Halide Perovskites and Their Analogues: Film Fabrication, Applications and Beyond

Metal halide perovskites emerge as promising semiconductors for optoelectronic devices due to ease of fabrication, attractive photophysical properties, their low cost, highly tunable material properties, and high performance. High-quality thin films of metal halide perovskites are the basis of most of these applications including solar cells, light-emitting diodes, photodetectors, and electronic memristors. A typical fabrication method for perovskite thin films is the solution method, which has several limitations in device reproducibility, adverse environmental impact, and utilization of raw materials. Thermal evaporation holds great promise in addressing these bottlenecks in fabricating high-quality halide perovskite thin films. It also has high compatibility with mass-production platforms that are well-established in industries. This review first introduces the basics of the thermal evaporation method with a particular focus on the critical parameters influencing the thin film deposition. The research progress of the fabrication of metal halide perovskite thin films is further summarized by different thermal evaporation approaches and their applications in solar cells and other optoelectronic devices. Finally, research challenges and future opportunities for both fundamental research and commercialization are discussed.

In Situ Unveiling of the Resistive Switching Mechanism of Halide Perovskite-Based Memristors

The organic-inorganic halide perovskite has become one of the most promising candidates for next-generation memory devices, i.e. memristors, with excellent performance and solution-processable preparation. Yet, the mechanism of resistive switching in perovskite-based memristors remains ambiguous due to a lack of in situ visualized characterization methods. Here, we directly observe the switching process of perovskite memristors with in situ photoluminescence (PL) imaging microscopy under an external electric field. Furthermore, the corresponding element composition of conductive filaments (CFs) is studied, indicating that the metallic CFs with respect to the activity of the top electrode are essential for device performance. Finally, electrochemical impedance spectroscopy (EIS) is conducted to reveal that the transition of ion states is associated with the formation of metallic CFs. This study provides in-depth insights into the switching mechanism of perovskite memristors, paving a pathway to develop and optimize high-performance perovskite memristors for large-scale applications.

Quasi-2D Lead-Tin Perovskite Memory Devices Fabricated by Blade Coating

Two terminal passive devices are regarded as one of the promising candidates to solve the processor-memory bottleneck in the Von Neumann computing architectures. Many different materials are used to fabricate memory devices, which have the potential to act as synapses in future neuromorphic electronics. Metal halide perovskites are attractive for memory devices as they display high density of defects with a low migration barrier. However, to become promising for a future neuromorphic technology, attention should be paid on non-toxic materials and scalable deposition processes. Herein, it is reported for the first time the successful fabrication of resistive memory devices using quasi-2D tin-lead perovskite of composition (BA)2 MA4 (Pb0.5 Sn0.5 )5 I16 by blade coating. The devices show typical memory characteristics with excellent endurance (2000 cycles), retention (105  s), and storage stability (3 months). Importantly, the memory devices successfully emulate synaptic behaviors such as spike-timing-dependent plasticity, paired-pulse facilitation, short-term potentiation, and long-term potentiation. A mix of slow (ionic) transport and fast (electronic) transport (charge trapping and de-trapping) is proven to be responsible for the observed resistive switching behavior.

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.

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.

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.

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.

Nanostructured perovskites for nonvolatile memory devices

Perovskite materials have driven tremendous advances in constructing electronic devices owing to their low cost, facile synthesis, outstanding electric and optoelectronic properties, flexible dimensionality engineering, and so on. Particularly, emerging nonvolatile memory devices (eNVMs) based on perovskites give birth to numerous traditional paradigm terminators in the fields of storage and computation. Despite significant exploration efforts being devoted to perovskite-based high-density storage and neuromorphic electronic devices, research studies on materials' dimensionality that has dominant effects on perovskite electronics' performances are paid little attention; therefore, a review from the point of view of structural morphologies of perovskites is essential for constructing perovskite-based devices. Here, recent advances of perovskite-based eNVMs (memristors and field-effect-transistors) are reviewed in terms of the dimensionality of perovskite materials and their potentialities in storage or neuromorphic computing. The corresponding material preparation methods, device structures, working mechanisms, and unique features are showcased and evaluated in detail. Furthermore, a broad spectrum of advanced technologies (e.g., hardware-based neural networks, in-sensor computing, logic operation, physical unclonable functions, and true random number generator), which are successfully achieved for perovskite-based electronics, are investigated. It is obvious that this review will provide benchmarks for designing high-quality perovskite-based electronics for application in storage, neuromorphic computing, artificial intelligence, information security, etc.

Controlling the Grain Size of Dion-Jacobson-Phase Two-Dimensional Layered Perovskite for Memory Application

Organic-inorganic halide perovskites (OIHPs) have emerged as an active layer for resistive switching memory (RSM). Among various OIHPs, two-dimensional OIHPs are advantageous in RSMs because of their stability. This stability can be further improved using two-dimensional Dion-Jacobson OIHPs. Moreover, OIHP-based RSMs operated by the formation of halide-ion filaments are affected by grain boundaries because they can act as a shortcut for ion migration. Therefore, it is essential to control the grains in OIHPs for reliable memory operation. Here, we present RSMs using Dion-Jacobson OIHP with controlled grain sizes. The grain sizes of the OIHP are effectively controlled by adjusting the ratio of the N,N-dimethylformamide and dimethyl sulfoxide. The controlled grain sizes can modulate the paths for halide ion migration, which enables the change of the on/off ratio in RSM. In addition, cross-point array structure is essential for high-density memory applications. However, in the cross-point array structure, unwanted current flow through unselected memory cells can happen due to sneak-current paths, so it is necessary to suppress leakage current from neighboring cells by adopting selector devices. We demonstrate the application of selector devices to OIHP-based RSMs to prevent sneak current paths. These results provide the potential of OIHP for use in high-density memory applications.

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.

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.

One-Dimensional (NH=CINH3)3PbI5 Perovskite for Ultralow Power Consumption Resistive Memory

Organic-inorganic hybrid perovskites (OIHPs) have proven to be promising active layers for nonvolatile memories because of their rich abundance in earth, mobile ions, and adjustable dimensions. However, there is a lack of investigation on controllable fabrication and storage properties of one-dimensional (1D) OIHPs. Here, the growth of 1D (NH=CINH3)3PbI5 ((IFA)3PbI5) perovskite and related resistive memory properties are reported. The solution-processed 1D (IFA)3PbI5 crystals are of well-defined monoclinic crystal phase and needle-like shape with the length of about 6 mm. They exhibit a wide bandgap of 3 eV and a high decomposition temperature of 206°C. Moreover, the (IFA)3PbI5 films with good uniformity and crystallization were obtained using a dual solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). To study the intrinsic electric properties of this anisotropic material, we constructed the simplest memory cell composed of only Au/(IFA)3PbI5/ITO, contributing to a high-compacted device with a crossbar array device configuration. The resistive random access memory (ReRAM) devices exhibit bipolar current-voltage (I-V) hysteresis characteristics, showing a record-low power consumption of ~0.2 mW among all OIHP-based memristors. Moreover, our devices own the lowest power consumption and "set" voltage (0.2 V) among the simplest perovskite-based memory devices (inorganic ones are also included), which are no need to require double metal electrodes or any additional insulating layer. They also demonstrate repeatable resistance switching behaviour and excellent retention time. We envision that 1D OIHPs can enrich the low-dimensional hybrid perovskite library and bring new functions to low-power information devices in the fields of memory and other electronics applications.

Enhanced resistive switching performance in yttrium-doped CH3NH3PbI3 perovskite devices

In this study, yttrium-doped CH₃NH₃PbI₃ (Y-MAPbI₃) and pure CH₃NH₃PbI₃ (MAPbI₃) perovskite films have been fabricated using a one-step solution spin coating method in a glove box. X-ray diffractometry and field-emission scanning electron microscopy were used to characterize the crystal structures and morphologies of perovskite films, respectively. It was found that the orientation of the crystal changed and the grains became more uniform in Y-MAPbI₃ film, compared with the pure MAPbI₃ perovskite film. The films were used to prepare the resistive switching memory devices with the device structure of Al/Y-MAPbI₃ (MAPbI₃)/ITO-glass. The memory performance of both devices was studied and showed a bipolar resistive switching behavior. The Al/MAPbI₃/ITO device had an endurance of about 328 cycles. In contrast, the Al/Y-MAPbI₃/ITO device exhibited an enhanced performance with a long endurance up to 3000 cycles. Moreover, the Al/Y-MAPbI₃/ITO device also showed a higher ON/OFF ratio of over 10³, long retention time (≥10⁴ s), lower operation voltage (±0.5 V) and outstanding reproducibility. Additionally, the conduction mechanism of the high resistance state transformed from space-charge limited current for a Y free device to the Schottky emission after Y doping. The present results indicate that the Al/Y-MAPbI₃/ITO device has a great potential to be used in high-performance memory devices.

Towards High-Performance Resistive Switching Behavior through Embedding a D-A System into 2D Imine-Linked Covalent Organic Frameworks

Developing new materials for the fabrication of resistive random-access memory is of great significance in this period of big data. Herein, we present a novel design strategy of embedding donor (D) and acceptor (A) fragments into imine-linked frameworks to construct resistive switching covalent organic frameworks (COFs) for high-performance memristors. Two D-A-type two-dimensional COFs, COF-BT-TT and COF-TT-TVT, were designed and synthesized using a conventional solvothermal approach, and high-quality thin films of these materials deposited on ITO substrate exhibited great potential as an active layer for memristors. Rewritable memristors based on 100 nm thick COF-TT-BT and COF-TT-TVT films showed a high ON/OFF current ratio (ca. 10⁵ and 10⁴ ) and low driving voltage (1.30 and 1.60 V). The cycle period and retention time for COF-TT-BT-based rewritable devices were as high as 319 cycles and 3.3×10⁴  s at a constant voltage of 0.1 V (160 cycles and 1.2×10⁴  s for the COF-TT-TVT memristor).

Advances in Flexible Memristors with Hybrid Perovskites

Hybrid organic-inorganic metal halide perovskite (HOIP)-based memristors have captured strong attention not only as an emerging candidate for next-generation high-density information storage technology but also for use in healthcare technology and the Internet of Things (IoT) because of their unique properties: low weight, flexibility, compatibility, stretchability, and low power consumption. In this Perspective, we review the recent advances of various aspects of flexible memristors focusing on the selection of the flexible substrates, materials, interfaces, several resistive switching mechanisms, and different methodologies of perovskite growth. The current state of the art of the memristor as an artificial synapse, light-induced resistive switching, and logic gates is comprehensively and systematically reviewed. Finally, we briefly discuss the stability factors of perovskites and present the conclusion with a broad outlook on the progress and challenges in the field of perovskite-based flexible memristors.

Voltage-Tunable Ultra-Steep Slope Atomic Switch with Selectivity over 1010

Atomic switch-based selectors, which utilize the formation of conductive filaments by the migration of ions, are researched for cross-point array architecture due to their simple structure and high selectivity. However, the difficulty in controlling the formation of filaments causes uniformity and reliability issues. Here, a multilayer selector with Pt/Ag-doped ZnO/ZnO/Ag-doped ZnO/Pt structure by the sputtering process is presented. A multilayer structure enables control of the filament formation by preventing excessive influx of Ag ions. The multilayer selector device exhibits a high on-current density of 2 MA cm^-2 , which can provide sufficient current for the operation with the memory device. Also, the device exhibits high selectivity of 10¹⁰ and a low off-current of 10^-13 A. The threshold voltage of selector devices can be controlled by modulating the thickness of the ZnO layer. By connecting a multilayer selector device to a resistive switching memory, the leakage current of the memory device can be reduced. These results demonstrate that a multilayer structure can be used in a selector device to improve selectivity and reliability for use in high-density memory devices.

Humidity Effect on Resistive Switching Characteristics of the CH3NH3PbI3 Memristor

Organic-inorganic hybrid halide perovskites (OIHPs) with inherent mixed ionic-electronic conduction ability have been proposed as promising candidates for memristors with unique optoelectronic characteristics. Despite the great achievements toward understanding the working mechanism and exploring their functionality as water-sensitive materials, the humidity effect on the resistive switching (RS) characteristics still remains to be studied. This study investigates the humidity effect on the RS characteristics of Au/CH₃NH₃PbI₃/FTO memristor. The memristor works well at moderate relative humidity (RH, <75%) and degrades rapidly at higher RH of 90%. An obvious decrease in low resistance states on increasing the RH level is observed, which could be attributed to water-induced reduction of the iodide migration barrier. Raman and X-ray diffraction analyses indicate that the migration barrier reduction possibly originated from the weakening of the Pb-I bond caused by the intercalation of water molecules into the crystal lattice. The humidity-sensitive RS characteristics of the memristor could extend the scope of OIHP application for sensing and security applications and also prompt researchers to pay attention to the humidity effect on memristor devices with OIHPs.

Designing zero-dimensional dimer-type all-inorganic perovskites for ultra-fast switching memory

Resistive switching memory that uses halide perovskites (HP) has been considered as next-generation storage devices due to low operation voltage and high on/off ratio. However, the memory still faces challenges for stable operation with fast switching speed, which hinders the practical application. Thus, it should be considered from the stage of designing the HP for memory applications. Here, we design the perovskite memory using a high-throughput screening based on first-principles calculations. Total 696 compositions in four different crystal structures are investigated and essential parameters including stability, vacancy formation, and migration are considered as the descriptor. We select dimer-Cs3Sb2I9 as an optimal HP for memory; the device that uses dimer-Cs3Sb2I9 has ultra-fast switching speed (~20 ns) compared to the device that uses layer-Cs3Sb2I9 (>100 ns). The use of lead-free perovskite avoids environmental problems caused by lead in perovskite. These results demonstrate the feasibility to design the memory with ultra-fast switching speed.

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.

Advances in Halide Perovskite Memristor from Lead-Based to Lead-Free Materials

Memristors have attracted considerable attention as one of the four basic circuit elements besides resistors, capacitors, and inductors. Especially, the nonvolatile memory devices have become a promising candidate for the new-generation information storage, due to their excellent write, read, and erase rates, in addition to the low-energy consumption, multistate storage, and high scalability. Among them, halide perovskite (HP) memristors have great potential to achieve low-cost practical information storage and computing. However, the usual lead-based HP memristors face serious problems of high toxicity and low stability. To alleviate the above issues, great effort has been devoted to develop lead-free HP memristors. Here, we have summarized and discussed the advances in HP memristors from lead-based to lead-free materials including memristive properties, stability, neural network applications, and memristive mechanism. Finally, the challenges and prospects of lead-free HP memristors have been discussed.

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.

Room-Temperature, Solution-Processed SiOx via Photochemistry Approach for Highly Flexible Resistive Switching Memory

Due to its high versatility and cost-effectiveness, solution process has a remarkable advantage over physical or chemical vapor deposition (PVD/CVD) methods in developing flexible resistive random-access memory (RRAM) devices. However, the reported solution-processed binary oxides, the most promising active layer materials for their compatibility with silicon-based semiconductor technology, commonly require high-temperature annealing (>145 °C) and the RRAMs based on them encounter insufficient flexibility. In this work, an amorphous and uniform SiO_x active layer was prepared by irradiating an inorganic polymer, perhydropolysilazane, with a vacuum ultraviolet of 172 nm at room temperature. The corresponding RRAM showed typical bipolar resistance switching with a forming-free behavior. The device on polyimide film exhibited outstanding flexibility with a minimum bending radius of 0.5 mm, and no performance degradation was observed after bending 2000 times with a radius of 2.3 mm, which is the best among the reported solution-processed binary oxide-based RRAMs and can even rival the performance of PVD/CVD-based devices. This room-temperature solution process and the afforded highly flexible RRAMs have vast prospects for application in smart wearable electronics.

Controllable deposition of organic metal halide perovskite films with wafer-scale uniformity by single source flash evaporation

Conventional solution-processing techniques such as the spin-coating method have been used successfully to reveal excellent properties of organic-inorganic halide perovskites (OHPs) for optoelectronic devices such as solar cell and light-emitting diode, but it is essential to explore other deposition techniques compatible with large-scale production. Single-source flash evaporation technique, in which a single source of materials of interest is rapidly heated to be deposited in a few seconds, is one of the candidate techniques for large-scale thin film deposition of OHPs. In this work, we investigated the reliability and controllability of the single-source flash evaporation technique for methylammonium lead iodide (MAPbI3) perovskite. In-depth statistical analysis was employed to demonstrate that the MAPbI3 films prepared via the flash evaporation have an ultrasmooth surface and uniform thickness throughout the 4-inch wafer scale. We also show that the thickness and grain size of the MAPbI3 film can be controlled by adjusting the amount of the source and number of deposition steps. Finally, the excellent large-area uniformity of the physical properties of the deposited thin films can be transferred to the uniformity in the device performance of MAPbI3 photodetectors prepared by flash evaporation which exhibited the responsivity of 0.2 A/W and detectivity of 3.82 × 1011 Jones.

Lead-Free Dual-Phase Halide Perovskites for Preconditioned Conducting-Bridge Memory

Organometallic and all-inorganic halide perovskites (HPs) have recently emerged as promising candidate materials for resistive switching (RS) nonvolatile memory due to their current-voltage hysteresis caused by fast ion migration. Lead-free and all-inorganic HPs have been researched for non-toxic and environmentally friendly RS memory devices. However, only HP-based devices with electrochemically active top electrode (TE) exhibit ultra-low operating voltages and high on/off ratio RS properties. The active TE easily reacts to halide ions in HP films, and the devices have a low device durability. Herein, RS memory devices based on an air-stable lead-free all-inorganic dual-phase HP (AgBi₂ I₇ -Cs₃ Bi₂ I₉ ) are successfully fabricated with inert metal electrodes. The devices with Au TE show filamentary RS behavior by conducting-bridge involving Ag cations in HPs with ultra-low operating voltages (<0.15 V), high on/off ratio (>10⁷ ), multilevel data storage, and long retention times (>5 × 10⁴ s). The use of a closed-loop pulse switching method improves reversible RS properties up to 10³ cycles with high on/off ratio above 10⁶ . With an extremely small bending radius of 1 mm, the devices are operable with reasonable RS characteristics. This work provides a promising material strategy for lead-free all-inorganic HP-based nonvolatile memory devices for practical applications.

Metal-Halide Perovskite Design for Next-Generation Memories: First-Principles Screening and Experimental Verification

Memory devices have been advanced so much, but still it is highly required to find stable and reliable materials with low-power consumption. Halide perovskites (HPs) have been recently adopted for memory application since they have advantages of fast switching based on ionic motion in crystal structure. However, HPs also suffer from poor stability, so it is necessary to improve the stability of HPs. In this regard, combined first-principles screening and experimental verification are performed to design HPs that have high environmental stability and low-operating voltage for memory devices. First-principles screening identifies 2D layered AB2X5 structure as the best candidate switching layer for memory devices, because it has lower formation energy and defect formation energy than 3D ABX3 or other layered structures (A3B2X7, A2BX4). To verify results, all-inorganic 2D layered CsPb2Br5 is synthesized and used in memory devices. The memory devices that use CsPb2Br5 show much better stability and lower operating voltages than devices that use CsPbBr3. These findings are expected to provide new opportunity to design materials for reliable device applications based on calculation, screening, and experimental verification.

Extremely Low Program Current Memory Based on Self-Assembled All-Inorganic Perovskite Single Crystals

Memory devices based on lead halide perovskite have attracted great interests because of their unique current-voltage hysteresis. However, current memory devices based on polycrystalline perovskites usually suffer from large intrinsic electronic current and parasitic leakage current due to the existence of grain boundaries, which further leads to high power consumption. Here, a low-power resistance switching random-access memory device is demonstrated by assembling single-crystalline CsPbBr₃ on Ag electrodes. The assembled structure serves as a bipolar nonvolatile resistance switching memory device with a low program current (∼10 nA), good endurance, long data retention (>10³ S), and big on/off ratio of ∼10³. The low program current results in a power of ∼3 × 10^-8 W, which is much lower than that of polycrystalline perovskite-based devices (10^-1-10^-6 W). It is found that the formation and annihilation of Ag and bromide vacancy conductive filaments contribute to the significant resistive switching effect. At a low resistive state, the conductive filaments originate from the accumulation of Br^- ions at the drain. Furthermore, the conductive filaments are proved to be a cone shape, shrinking from the drain to the source.

Roadmap on halide perovskite and related devices

Since the first report on solid-state perovskite solar cells (PSCs) with ∼10% power conversion efficiency (PCE) and 500 h-stability in 2012, tremendous effort has been being devoted to develop PSCs with higher PCE, longer stability and recycling hazardous lead waste. As a result, PCE over 23% was recorded in 2018 and stability over 10 000 h was reported. Beyond photovoltaics, lead halide perovskite materials demonstrated superb properties when they were applied to flat-panel x-ray detectors and non-volatile resistive switching memory. In this review, the progress of the lead halide perovskite in photovoltaics, x-ray imaging and memristors is investigated. Pb-based PSCs and non-Pb-based PSCs are compared, where technologies of non-Pb-based PSCs are not matured for commercialization. Pb-based PSCs were found to be highly suitable for both terrestrial and space photovoltaics. Higher sensitivity under low dose rate observed from the lead halide perovskite suggests a bright future for perovskite x-ray imaging systems. Moreover, high on/off ratio and low energy consumption observed in resistive switching enables perovskite to be a promising candidate for high density memristors.

Environmentally Robust Memristor Enabled by Lead-Free Double Perovskite for High-Performance Information Storage

Memristors are emerging as a rising star of new computing and information storage techniques. However, the practical applications are severely challenged by their instability toward harsh conditions, including high moisture, high temperatures, fire, ionizing irradiation, and mechanical bending. In this work, for the first time, lead-free double perovskite Cs₂ AgBiBr₆ is utilized for environmentally robust memristors, enabling highly efficient information storage. The memory performance of the typical indium-tin-oxide/Cs₂ AgBiBr₆ /Au sandwich-like memristors is retained after 1000 switching cycles, 10⁵ s of reading, and 10⁴ times of mechanical bending, comparable to other halide perovskite memristors. Most importantly, the memristive behavior remains robust in harsh environments, including humidity up to 80%, temperatures as high as 453 K, an alcohol burner flame for 10 s, and ⁶⁰ Co γ-ray irradiation for a dosage of 5 × 10⁵ rad (SI), which is not achieved by any other memristors and commercial flash memory techniques. The realization of an environmentally robust memristor from Cs₂ AgBiBr₆ with a high memory performance will inspire further development of robust electronics using lead-free double perovskites.

Enhanced Switching Ratio and Long-Term Stability of Flexible RRAM by Anchoring Polyvinylammonium on Perovskite Grains

The ON/OFF ratio and long-term stability are two important issues for flexible organic-inorganic hybrid perovskite (OHP) resistive random access memory (RRAM) for practical applications. In this work, polyvinylammonium (PVAm) is applied to partially replace methylamine ions (MA⁺) to fabricate the stable and flexible polymeric OHP RRAM devices, wherein PVAm acts as nucleation sites and the template for crystalline growth of MAPbI₃ to tune the microscopic perovskite structure. Simultaneously, the multiple perovskite grain interfaces are strengthened through the long-carbochain polymeric backbone, hence producing a continuous and compact perovskite film. As a result, the PVAm-modified OHP RRAM device shows remarkable enhancement of the ON/OFF ratio, long-term stability, and flexibility compared with the unmodified OHP device. Specifically, the polymeric OHP device exhibits fast and stable nonvolatile resistive switching (RS) characteristics with an ON/OFF ratio of ∼10⁵ and a set voltage of -0.45 V under ambient conditions. Also, the distinct multilevel RS behavior can be realized in this device by controlling the compliance current in the SET process. Additionally, the unsealed polymeric OHP device manifests the striking long-term stability, which can still maintain the stable memory performance after 1 year exposure to the humid and thermal ambient environment. Furthermore, the flexible polymeric OHP device was also fabricated and affords the excellent bending endurance behavior by showing a reproducible RS property over 100-cycle bending experiments. This work provides a new perovskite-based material design strategy of polymeric OHP for stable and flexible RRAM devices with the high ON/OFF ratio.

Lead-Free Double Perovskite Cs2 SnX6 : Facile Solution Synthesis and Excellent Stability

Long-term instability and possible lead contamination are the two main issues limiting the widespread application of organic-inorganic lead halide perovskites. Here a facile and efficient solution-phase method is demonstrated to synthesize lead-free Cs₂ SnX₆ (X = Br, I) with a well-defined crystal structure, long-term stability, and high yield. Based on the systematic experimental data and first-principle simulation results, Cs₂ SnX₆ displays excellent stability against moisture, light, and high temperature, which can be ascribed to the unique vacancy-ordered defect-variant structure, stable chemical compositions with Sn⁴⁺ , as well as the lower formation enthalpy for Cs₂ SnX₆ . Additionally, photodetectors based on Cs₂ SnI₆ are also fabricated, which show excellent performance and stability. This study provides very useful insights into the development of lead-free double perovskites with high stability.

Room-Temperature Cubic Phase Crystallization and High Stability of Vacuum-Deposited Methylammonium Lead Triiodide Thin Films for High-Efficiency Solar Cells

Methylammonium lead triiodide (MAPI) has emerged as a high-performance photovoltaic material. Common understanding is that at room temperature, it adopts a tetragonal phase and it only converts to the perfect cubic phase around 50-60 °C. Most MAPI films are prepared using a solution-based coating process, yet they can also be obtained by vapor-phase deposition methods. Vapor-phase-processed MAPI films have significantly different characteristics than their solvent-processed analogous, such as relatively small crystal-grain sizes and short excited-state lifetimes. However, solar cells based on vapor-phase-processed MAPI films exhibit high power-conversion efficiencies. Surprisingly, after detailed characterization it is found that the vapor-phase-processed MAPI films adopt a cubic crystal structure at room temperature that is stable for weeks, even in ambient atmosphere. Furthermore, it is demonstrated that by tuning the deposition rates of both precursors during codeposition it is possible to vary the perovskite phase from cubic to tetragonal at room temperature. These findings challenge the common belief that MAPI is only stable in the tetragonal phase at room temperature.

The effect of compositional engineering of imidazolium lead iodide on the resistive switching properties

We report here resistive switching memory characteristics of imidazolium lead iodide depending on the molar ratio of PbI2 to imidazolium iodide (ImI), that is, PbI2 : ImI = 1 : 0, 1 : 0.5, 1 : 1, 1 : 2, 1 : 3 and 0 : 1. X-ray diffraction confirms that the stoichiometric composition results in a hexagonal structure of (Im)PbI3, showing a one-dimensional face-sharing [PbI3-] chain. Bipolar resistive switching characteristics are observed regardless of the mixing ratio, where the forming process is required prior to SET and RESET processes at around +0.2 V and -0.2 V, respectively. The ON/OFF ratio is increased from 106 to 109 as the ImI content is increased due to the increased HRS associated with the pronounced insulating characteristics by ImI, whereas, the stoichiometric (Im)PbI3 exhibits 5 times longer endurance (103) and an order of magnitude longer retention time (104 s) as compared to other compositions. Multilevel data storage capability is confirmed by changing the compliance current. The low resistance state (LRS) and the high resistance state (HRS) are associated with Ohmic conduction and Schottky conduction, respectively. Density functional theory (DFT) calculation reveals that the defect formation energy of iodine vacancy is estimated to be low indicating that (Im)PbI3 has a sufficient concentration of iodide vacancy for filament formation. Further energy barrier calculations show that iodide migration preferentially occurs along the 1-dimensional [234] crystallographic direction rather than the interlayer [130] direction. A good performance of the (Im)PbI3-based memristor is thus related to the low defect formation energy of iodide vacancy and the preferential growth of the filament along the 1-dimensional chain.

High-Performance Nanofloating Gate Memory Based on Lead Halide Perovskite Nanocrystals

Lead halide perovskites have been extensively investigated in a host of optoelectronic devices, such as solar cells, light-emitting diodes, and photodetectors. The halogen vacancy defects arising from the halogen-poor growth environment are normally regarded as an unfavorable factor to restrict the device performance. Here, for the first time, we demonstrate the utilization of the vacancy defects in lead halide perovskite nanostructures for achieving high-performance nanofloating gate memories (NFGMs). CH₃NH₃PbBr₃ nanocrystals (NCs) were uniformly decorated on the CdS nanoribbon (NR) surface via a facile dip-coating process, forming a CdS NR/CH₃NH₃PbBr₃ NC core-shell structure. Significantly, owing to the existence of sufficient carrier trapping states in CH₃NH₃PbBr₃ NCs, the hybrid device possessed an ultralarge memory window up to 77.4 V, a long retention time of 12 000 s, a high current ON/OFF ratio of 7 × 10⁷, and a long-term air stability for 50 days. The memory window of the device is among the highest for the low-dimensional nanostructure-based NFGMs. Also, this strategy shows good universality and can be extended to other perovskite nanostructures for the construction of high-performance NFGMs. This work paves the way toward the fabrication of new-generation, high-capacity nonvolatile memories using lead halide perovskite nanostructures.

Impact of Grain Sizes on Programmable Memory Characteristics in Two-Dimensional Organic-Inorganic Hybrid Perovskite Memory

Recently, organic-inorganic hybrid perovskites (OIHPs) have been used in resistive switching memory applications because of current-voltage hysteresis that originated from ion migration in the perovskite film. As the density of the memory devices continues to increase, the size of the devices approaches that of the individual grains of the polycrystalline films. Thus, the effects of the grain boundary and the grain size will become important to investigate the influence on the switching behaviors. Here, we report the effects of grain sizes on the resistive switching property of (C₄H₉NH₃)₂PbBr₄ (BA₂PbBr₄) films. The BA₂PbBr₄ films were formed by using sequential vapor deposition. First, a lead bromide (PbBr₂) film was deposited by thermal evaporation, and then the film was exposed to organic vapor to form BA₂PbBr₄ films. The grain sizes were controlled by changing the transformation temperatures ( T_T = 100, 150, and 200 °C). When the T_T values were 100, 150, and 200 °C, the grain sizes of BA₂PbBr₄ were ∼180 nm, ∼1, and ∼30 μm, respectively. In the memory device based on BA₂PbBr₄, the off current decreased from ∼10^-4 to ∼10^-8 A as the grain size increased from ∼180 nm to ∼30 μm. This method to synthesize BA₂PbBr₄ films provides a simple way to control the grain sizes, and understanding of the effects of grain sizes on memory characteristics will provide an insight to improve the reliability of the OIHP-based memory as the electronic devices are scaled down to the sizes of grains.

High-Performance Solution-Processed Organo-Metal Halide Perovskite Unipolar Resistive Memory Devices in a Cross-Bar Array Structure

Resistive random access memories can potentially open a niche area in memory technology applications by combining the advantages of the long endurance of dynamic random-access memory and the long retention time of flash memories. Recently, resistive memory devices based on organo-metal halide perovskite materials have demonstrated outstanding memory properties, such as a low-voltage operation and a high ON/OFF ratio; such properties are essential requirements for low power consumption in developing practical memory devices. In this study, a nonhalide lead source is employed to deposit perovskite films via a simple single-step spin-coating method for fabricating unipolar resistive memory devices in a cross-bar array architecture. These unipolar perovskite memory devices achieve a high ON/OFF ratio up to 10⁸ with a relatively low operation voltage, a large endurance, and long retention times. The high-yield device fabrication based on the solution-process demonstrated here will be a step toward achieving low-cost and high-density practical perovskite memory devices.

Organic and hybrid resistive switching materials and devices

This review presents a timely and comprehensive summary of organic and hybrid materials for nonvolatile resistive switching memory applications in the “More than Moore” era, with particular attention on their designing principles for electronic property tuning and flexible memory performance.

pH-Modulated memristive behavior based on an edible garlic-constructed bio-electronic device

A new type of memristive memory device with an edible garlic-constructed Ag/garlic/fluorine-doped SnO₂(FTO) structure for analog neuromorphic sensor applications was designed.

Infrared-Sensitive Memory Based on Direct-Grown MoS2 -Upconversion-Nanoparticle Heterostructure

Photonic memories as an emerging optoelectronic technology have attracted tremendous attention in the past few years due to their great potential to overcome the von Neumann bottleneck and to improve the performance of serial computers. Nowadays, the decryption technology for visible light is mature in photonic memories. Nevertheless, near-infrared (NIR) photonic memristors are less progressed. Herein, an NIR photonic memristor based on MoS₂ -NaYF₄ :Yb³⁺ , Er³⁺ upconversion nanoparticles (UCNPs) nanocomposites is designed. Under excitation by 980 nm NIR light, the UCNPs show emissions well overlapping with the absorption band of the MoS₂ nanosheets. The heterostructure between the MoS₂ and the UCNPs acting as excitons generation/separation centers remarkably improves the NIR-light-controlled memristor performance. Furthermore, in situ conductive atomic force microscopy is employed to elucidate the photo-modulated memristor mechanism. This work provides novel opportunities for NIR photonic memory that holds promise in future multifunctional robotics and electronic eyes.

Organic-Inorganic Hybrid Halide Perovskites for Memories, Transistors, and Artificial Synapses

Fascinating characteristics of halide perovskites (HPs), which cannot be seen in conventional semiconductors and metal oxides, have boosted the application of HPs in electronic devices beyond optoelectronics such as solar cells, photodetectors, and light-emitting diodes. Here, recent advances in HP-based memory and logic devices such as resistive-switching memories (i.e., resistive random access memory (RRAM) or memristors), transistors, and artificial synapses are reviewed, focusing on inherently exotic properties of HPs: i) tunable bandgap, ii) facile majority carrier control, iii) fast ion migration, and iv) superflexibility. Various fabrication techniques of HP thin films from solution-based methods to vacuum processes are introduced. Up-to-date work in the field, emphasizing the compositional flexibility of HPs, suggest that HPs are promising candidates for next-generation electronic devices. Taking advantages of their unique electrical properties, low-cost and low-temperature synthesis, and compositional and mechanical flexibility, HPs have enormous potential to provide a new platform for future electronic devices and explosively intensive studies will pave the way in finding new HP materials beyond conventional silicon-based semiconductors to keep up with "More-than-Moore" times.

Reset Voltage-Dependent Multilevel Resistive Switching Behavior in CsPb1- xBi xI3 Perovskite-Based Memory Device

All-inorganic CsPb_{1- x}Bi _xI₃ perovskite film was successfully fabricated by incorporating Bi³⁺ in CsPbI₃ to stabilize the cubic lattice. Furthermore, the perovskite film was applied to manufacture a simple Ag/CsPb_{1- x}Bi _xI₃/indium tin oxide (ITO) memory device with a bipolar resistive switching behavior. Nonvolatile, reliable, and reproducible switching properties are demonstrated through retention and endurance test under fully open-air conditions. The memory device also presents highly uniform and long-term stable characteristics. Importantly, by modulating the reset stop voltages, multilevel high-resistance states are observed for the first time in lead halide perovskite memory device. The resistive switching behavior is proposed to explain the formation and partial rupture of conductive multifilament that are dominated by the migration of iodine ions and their corresponding vacancies in perovskite film. This study suggests Ag/CsPb_{1- x}Bi _xI₃/ITO device potential application for multilevel data storage in a nonvolatile memory device.

Synergies of Electrochemical Metallization and Valance Change in All-Inorganic Perovskite Quantum Dots for Resistive Switching

The in-depth understanding of ions' generation and movement inside all-inorganic perovskite quantum dots (CsPbBr₃ QDs), which may lead to a paradigm to break through the conventional von Neumann bottleneck, is strictly limited. Here, it is shown that formation and annihilation of metal conductive filaments and Br^- ion vacancy filaments driven by an external electric field and light irradiation can lead to pronounced resistive-switching effects. Verified by field-emission scanning electron microscopy as well as energy-dispersive X-ray spectroscopy analysis, the resistive switching behavior of CsPbBr₃ QD-based photonic resistive random-access memory (RRAM) is initiated by the electrochemical metallization and valance change. By coupling CsPbBr₃ QD-based RRAM with a p-channel transistor, the novel application of an RRAM-gate field-effect transistor presenting analogous functions of flash memory is further demonstrated. These results may accelerate the technological deployment of all-inorganic perovskite QD-based photonic resistive memory for successful logic application.

A non-volatile "programmable" transparent multilevel ultra-violet perovskite photodetector

Due to their outstanding physical properties, perovskite materials are considered to be promising semiconductors for next-generation optoelectronics. However, these materials are often unstable under an ambient atmosphere and ultra-violet illumination. Therefore, the construction of an air-stable visible light transparent perovskite-based ultra-violet photodetector is still highly challenging. In this study, we go beyond the conventional operation of photodetectors by utilizing the undesired hysteresis loop in the typical current-voltage characteristics of perovskites and design a (C4H9NH3)2PbBr4-based high-performance visible transparent programmable ultra-violet photodetector. The photodetector shows multiple operating levels and can switch from one level to another with a short electric pulse. The photodetector exhibits a fast response time of ∼2 ms, good responsivity of ∼32 mA W-1 and detectivity of 8.5 × 108 Jones with a low working voltage of 0.5 V. Moreover, the photodetector shows long-term stability, and the optoelectronic performance is retained under ambient conditions. This breakthrough in the controlled tunable features opens a new avenue for the development of multipurpose transparent optoelectronic devices.

Enhancement of resistive switching properties in Al2O3 bilayer-based atomic switches: multilevel resistive switching

Atomic switches are considered to be building blocks for future non-volatile data storage and internet of things. However, obtaining device structures capable of ultrahigh density data storage, high endurance, and long data retention, and more importantly, understanding the switching mechanisms are still a challenge for atomic switches. Here, we achieved improved resistive switching performance in a bilayer structure containing aluminum oxide, with an oxygen-deficient oxide as the top switching layer and stoichiometric oxide as the bottom switching layer, using atomic layer deposition. This bilayer device showed a high on/off ratio (10⁵) with better endurance (∼2000 cycles) and longer data retention (10⁴ s) than single-oxide layers. In addition, depending on the compliance current, the bilayer device could be operated in four different resistance states. Furthermore, the depth profiles of the hourglass-shaped conductive filament of the bilayer device was observed by conductive atomic force microscopy.