Next-generation Nonvolatile Memory Research Articles

Conversion between digital and analog resistive switching behaviors and logic display application of photoresponsive ZnO nanorods-based memristor

Memristors have shown great application prospects in next-generation non-volatile memory (NVMs) and brain-inspired computing systems, but various application prospects have different requirements for device performance. Currently, it is difficult to precisely regulate the conversion of memristive effects between analog and digital due to the complex resistive switching mechanism. In this work, size-controlled ZnO nanorods was achieved by adjusting the concentration of the surfactant polyethyleneimine (PEI), and further research was conducted for the memristive effect of the as-prepared memristors based on ZnO nanorods with different sizes. The results showed that PEI accelerates the protonation process, leading to the increase of OH– ions, which further leads to the transition of the memristive effect of the as-prepared device from digital to analog as the PEI concentration increases. Moreover, the optical controlled logic display function was achieved in the memristor based on the light-sensitive properties of the ZnO nanorods. Therefore, this work lays the foundation that the memristor with analog and digital memristive effect can control and enrich the application prospects of memristor.

A BaTiO3-based flexible ferroelectric capacitor for non-volatile memories

BaTiO3 (BTO) ferroelectric films, which are renowned for their lead-free compositions, superior stability, and absence of a wake-up effect, are promising candidate materials in the field of non-volatile memories. However, the prerequisites for high-temperature conditions in the fabrication of ferroelectric thin films impose constraints on the substrate choice, which has limited the advancement in non-volatile memories based on single-crystal flexible BTO films with robust ferroelectric properties. Herein, a technique has been developed for the fabrication of flexible devices using a pulsed laser deposition system. BTO ferroelectric films have then been deposited onto a flexible mica substrate, with SrTiO3 (STO) serving as a buffer layer. The obtained flexible BTO devices exhibited excellent ferroelectricity, with a maximum polarization (2Pmax) of up to 42.58 μC/cm2 and a remnant polarization (2Pr) of up to 21.39 μC/cm2. Furthermore, even after 1,000 bending cycles, the bipolar switching endurance remained high at 1012 cycles. After 104 s, the flexible BTO device still maintained excellent polarization characteristics. These results make the flexible BTO ferroelectric thin film a potential candidate for the next generation of non-volatile memories.

Phase-change heterostructure with HfTe2 confinement sublayers for enhanced thermal efficiency and low-power operation through Joule heating localization

Although phase-change random-access memory (PCRAM) is a promising next-generation nonvolatile memory technology, challenges remain in terms of reducing energy consumption. This is primarily because the high thermal conductivities of phase-change materials (PCMs) promote Joule heating dissipation. Repeated phase transitions also induce long-range atomic diffusion, limiting the durability. To address these challenges, phase-change heterostructure (PCH) devices that incorporate confinement sublayers based on transition-metal dichalcogenide materials have been developed. In this study, we engineered a PCH device by integrating HfTe2, which has low thermal conductivity and excellent stability, into the PCM to realize PCRAM with enhanced thermal efficiency and structural stability. HEAT simulations were conducted to validate the superior heat confinement in the programming region of the HfTe2-based PCH device. Moreover, electrical measurements of the device demonstrated its outstanding performance, which was characterized by a low RESET current (∼1.6 mA), stable two-order ON/OFF ratio, and exceptional cycling endurance (∼2 × 107). The structural integrity of the HfTe2 confinement sublayer was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy. The material properties, including electrical conductivity, cohesive energy, and electronegativity, substantiated these findings. Collectively, these results revealed that the HfTe2-based PCH device can achieve significant improvements in performance and reliability compared with conventional PCRAM devices.

Multi-bit MRAM based high performance neuromorphic accelerator for image classification

Binary neural networks (BNNs) are the most efficient solution to bridge the design gap of the hardware implementation of neural networks in a resource-constrained environment. Spintronics is a prominent technology among emerging fields for next-generation on-chip non-volatile memory. Spin transfer torque (STT) and spin-orbit torque (SOT) based magnetic random-access memory (MRAM) offer non-volatility and negligible static power. Over the last few years, STT and SOT-based multilevel spintronic memories have emerged as a promising solution to attain high storage density. This paper presents the operation principle and performance evaluation of spintronics-based single-bit STT and SOT MRAM, dual-level cells, three-level cells (TLCs), and four-level cells. Further, multi-layer perceptron architectures have been utilized to perform MNIST image classification with these multilevel devices. The performance of the complete system level consisting of crossbar arrays with various MRAM bit cells in terms of area, energy, and latency is evaluated. The throughput efficiency of the BNN accelerator using TLCs is 26.6X, and 3.61X higher than conventional single-bit STT-MRAM, and SOT-MRAM respectively.

Influence of interface on the domain polarization orientation in ferroelectric Hf0.5Zr0·5O2 thin films

Ferroelectric HfO2-based materials have attracted extensive attention in the research of next-generation nonvolatile memories and logic devices due to their superior scaling properties and compatibility with the CMOS process. However, forming the ferroelectric metastable phase in the thin films of a few nanometers requires clamping of the top and bottom electrodes. As a result, the interface can significantly impact domain structure and polarization, leading to imprinting effects and non-uniform space charge distribution. Here, we have demonstrated how the interface affects the ferroelectric polarization in Hf0.5Zr0·5O2 (HZO) thin films produced by ALD and the physical mechanisms behind it. We found that by regulating the quantity of oxygen vacancy content at the top and bottom interfaces of TiN/HZO/TiN ferroelectric capacitors, it is possible to achieve inversion of polarization orientation. By using a spherical aberration-corrected transmission electron microscope and first-principles calculation, we identified that the internal electric field generated by the accumulation of oxygen vacancies at an interface and the asymmetrical electrostatic energy of the interfacial T-phase layer jointly play a role in the ferroelectric polarization orientation. Our results will significantly help the interface engineering of HfO2-based ferroelectric thin films and devices.

Fabrication of high quality lead-free double perovskite Cs2AgBiBr6 thin film and its application in memristor with ultralow operation voltage

Recently, the lead-free double perovskite Cs2AgBiBr6 has been considered as a promising candidate for next-generation nonvolatile memory and artificial synapse devices due to its high stability and low toxicity compared to its lead-based counterparts. In this work, we developed a simple and effective method to produce high-quality lead-free double perovskite Cs2AgBiBr6 thin films without pinholes and particles by applying a low-pressure assisted method under ambient condition with a relative humidity (RH) of about 45%. The formation of pinholes and Ag precipitation in the perovskite Cs2AgBiBr6 films is effectively suppressed by the proper ratio of N,N-dimenthylformamide (DMF) mixed in dimethyl sulfoxide (DMSO) solvents. Furthermore, the grain size of the Cs2AgBiBr6 films can be significantly increased by increasing the post-annealing temperature. Finally, a sandwiched structure memristor with an ITO/Cs2AgBiBr6/Ta configuration was successfully demonstrated, featuring ultralow operation voltage (V Set ∼ 57 ± 23 mV, V Reset ∼ −692 ± 68 mV) and satisfactory memory window (the ratio of R HRS/R LRS ∼ 10 times), which makes it suitable for low-power consumption information storage devices.

Ferroelectricity in twisted double bilayer graphene

Two-dimensional (2D) ferroelectrics can maintain electrical polarization up to room temperature and are, therefore, promising for next-generation nonvolatile memories. Although natural 2D ferroelectrics are few, moiré superlattices provide us with a generalized method to construct ferroelectrics from non-ferroelectric parent materials. We report a realization of ferroelectric hysteresis in an AB-BA stacked twisted double bilayer graphene (TDBG) system. The ferroelectric polarization is prominent at zero external displacement field and reduces upon increasing displacement fields. TDBG in the AB-BA configuration is an intriguing system, which facilitates ferroelectricity even without the assistance of any boron nitride layers; however, in the AB-AB stacking case, the development of polarization necessitates the presence of a second superlattice induced by the adjacent boron nitride layer. Therefore, twisted multilayer graphene offers us a fascinating field to explore 2D ferroelectricity.

Thermally-induced nanoscale phase change in chalcogenide glass Cr2Ge2Te6 revealed by scanning tunneling microscopy

Cr2Ge2Te6 (CrGT) is viewed as an important phase change material (PCM) for next-generation nonvolatile memory devices because of its superior properties, e.g., high thermal stability and low operation energy, compared to conventional PCMs. However, the phase change mechanism of CrGT remains unsolved, especially at the nanoscale. Here, we investigated thermally induced nanoscale phase changes of CrGT thin films using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). By performing statistical analysis of the measured STM topographic and STS data, we evaluated the inhomogeneity and distribution of the phase change characteristics of CrGT thin films. We also related the nanoscale phase change properties of CrGT to macroscopic phase changes by comparing the STM and STS results with experimental data from Raman spectroscopy.

Selector-less crossbar array resistive RAM based on TiO2 fabricated by photochemical metal-organic deposition

In this study, we demonstrated a TiO2-based 32 × 32 crossbar array resistive RAM (ReRAM), a promising candidate for next-generation non-volatile memory (NVM), by utilizing a photochemical metal-organic deposition (PMOD) process. We achieved an interface-type resistive switching device with rectifying characteristics by controlling the oxidation state of directly patterned TiOx films through post-heat treatment. The photochemical reaction induced by UV in the PMOD process and the anatase phase formation during the post-heat treatment were analyzed using Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). XPS analysis revealed the immediate formation of Ti peroxide post-PMOD process, underscoring the efficacy of post-heat treatments in controlling oxidation states. Employing 350 °C annealed TiOX as the active material, we successfully fabricated a high-yield (93%), selectorless 32 × 32 crossbar array architecture for ReRAM. Our findings highlight the PMOD process as a viable, cost-effective alternative for memory devices, offering optimized oxidation states crucial for the performance of redox-based ReRAM.

(Invited) Fabrication Technique of Ferroelectric HfxZr1−XO2 Thin Films Using ALD-ZrO2 Nucleation Layers

Ferroelectric HfxZr1−xO2 (HZO) thin films have attracted considerable attention towards high-density and low-power ferroelectric memory devices of ferroelectric random access memory (FeRAM) and ferroelectric field-effect transistors (FeFETs) [1]. To obtain ferroelectric orthorhombic (O) phase of HZO films, several techniques have been investigated, such as the TiN stressor layer technique [2] and controlled annealing conditions [3]. On the other hand, we pay attention to the ZrO2 nucleation layer technique because ZrO2 films deposited by atomic layer deposition (ALD) method formed a nanocrystalline structure and consisted dominantly of O, tetragonal (T), and cubic (C) phases, whose lattice constants are considerably close to that of ferroelectric O phase for HfO2 [4]. In this paper, we report the crystallinity and ferroelectricity of HZO films fabricated using the ZrO2 nucleation layer technique for metal-ferroelectric-metal (MFM) and metal-ferroelectric-semiconductor (MFS) capacitors.First, four types of MFM capacitors of TiN/HZO/TiN (MFM w/o), TiN/HZO/bottom-ZrO2/TiN (MFM B-ZrO2), TiN/top-ZrO2/HZO/TiN (MFM T-ZrO2), and TiN/top-ZrO2/HZO/bottom-ZrO2/TiN (MFM D-ZrO2) were systematically investigated for the FeRAM applications [5]. The thicknesses of the ALD-grown HZO and ZrO2 films were 10 and 2 nm, respectively. The post-deposition annealing was performed at 600°C. The remanent polarization (2P r = P r + − P r −) of the MFM capacitors increased in the following order: MFM w/o (12 µC/cm2) < MFM B-ZrO2 (15 µC/cm2) < MFM T-ZrO2 (23 µC/cm2) < MFM D-ZrO2 (29 µC/cm2), while all capacitors showed almost the same coercive electric field (E c) value of around 1.2 MV/cm. Therefore, maximum 2P rvalue of the MFM capacitor was obtained using the top- and bottom-ZrO2 nucleation layers. For the MFM capacitors with ZrO2 nucleation layers, epitaxial-like grain growth of the HZO film occurred on the nanocrystalline top- and bottom-ZrO2 layers. Moreover, the relative ratio of O/T/C phases in the ferroelectric film, which was estimated using the peak area ratio of O(111)/T(101)/C(111)/{M(−111)+ O(111)/T(101)/C(111)+M(111)}, increased in the following order: MFM w/o < MFM B-ZrO2 < MFM T-ZrO2 < MFM D-ZrO2. Therefore, the top- and bottom-ZrO2 layers play an important role as nucleation layers for the crystallization of the HZO film, resulting in a larger relative ratio of O/T/C phases in the ferroelectric film compared to w/o. Moreover, these results indicate that the top-ZrO2 layer was more effective to form the ferroelectric phase compared to the bottom-ZrO2 layer.Next, two types of MFS capacitors of TiN/HZO/Si (MFS w/o) and TiN/top-ZrO2/HZO/Si (MFS T-ZrO2) were fabricated by low-temperature processes at 300°C of ALD and post-metallization annealing (PMA) for the FeFET applications [6]. The thicknesses of both HZO and ZrO2 films were 10 nm. Both MFS w/o and MFS T-ZrO2 were found to form an extremely thin SiO2 interfacial layer with a thickness of one or two monolayers between the HZO film and Si substrate due to a low temperature fabrication process of 300°C. The HZO film of the MFS T-ZrO2 formed O/T/C phases even with a low thermal budget of 300°C, while that of the MFS w/o had an amorphous structure. This result is attributed to the beneficial role of the nanocrystalline top-ZrO2 nucleation layer for the crystallization of an amorphous HZO film during the PMA process. Therefore, a higher 2P r value of 15 µC/cm2 was obtained for the MFS T-ZrO2 than that (2.2 µC/cm2) for the MFS w/o. Moreover, the endurance properties of the MFS T-ZrO2 were free from the wake-up effect and exhibited less degradation of switching polarization (P sw). This could be attributed to the insertion of a ZrO2 film at the TiN/HZO interface, which promoted the preferential formation of the ferroelectric orthorhombic phase and prevent the formation of oxygen vacancies at the ZrO2/HZO interface. Thus, we concluded that superior ferroelectricity with wake-up free properties and higher fatigue resistance of HZO-based MFS capacitors were achieved by using the ZrO2 nucleation layer technique.These results suggest that the fabrication technique of ferroelectric HZO films using nanocrystalline ALD-ZrO2 nucleation layers is one of the promising processes for the next-generation non-volatile memory device applications.This work was supported by JSPS KAKENHI (Nos. JP21J01667, JP20H02189, and JP18J22998) and MEXT Leading Initiative for Excellent Young Researchers (No. JPMXS0320220213).[1] T. Mikolajick et al., J. Appl. Phys. 129, 100901 (2021).[2] S. J. Kim, et al., Appl. Phys. Lett. 111, 242901 (2017).[3] S. Migita et al., Jpn. J. Appl. Phys. 58, SBBA07 (2019).[4] T. Onaya et. al., Appl. Phys. Express. 10, 081501 (2017).[5] T. Onaya et al., APL Mater. 7, 061107 (2019).[6] T. Onaya et al., APL Mater. 10, 051110 (2022).

Effect of Domain Structure and Dielectric Interlayer on Switching Speed of Ferroelectric Hf0.5Zr0.5O2 Film

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

High-performance van der Waals antiferroelectric CuCrP2S6-based memristors

Layered thio- and seleno-phosphate ferroelectrics, such as CuInP2S6, are promising building blocks for next-generation nonvolatile memory devices. However, because of the low Curie point, the CuInP2S6-based memory devices suffer from poor thermal stability (<42 °C). Here, exploiting the electric field-driven phase transition in the rarely studied antiferroelectric CuCrP2S6 crystals, we develop a nonvolatile memristor showing a sizable resistive-switching ratio of ~ 1000, high switching endurance up to 20,000 cycles, low cycle-to-cycle variation, and robust thermal stability up to 120 °C. The resistive switching is attributed to the ferroelectric polarization-modulated thermal emission accompanied by the Fowler–Nordheim tunneling across the interfaces. First-principles calculations reveal that the good device performances are associated with the exceptionally strong ferroelectric polarization in CuCrP2S6 crystal. Furthermore, the typical biological synaptic learning rules, such as long-term potentiation/depression and spike amplitude/spike time-dependent plasticity, are also demonstrated. The results highlight the great application potential of van der Waals antiferroelectrics in high-performance synaptic devices for neuromorphic computing.

Infrared Signatures for Phase Identification in Hafnium Oxide Thin Films.

Phase identification in HfO2-based thin films is a prerequisite to understanding the mechanisms stabilizing the ferroelectric phase in these materials, which hold great promise in next-generation nonvolatile memory and computing technology. While grazing-incidence X-ray diffraction is commonly employed for this purpose, it has difficulty unambiguously differentiating between the ferroelectric phase and other metastable phases that may exist due to similarities in the d-spacings, their low intensities, and the overlapping of reflections. Infrared signatures provide an alternative route. However, their use in phase identification remains limited because phase control has overwhelmingly been accomplished via substituents, thereby convoluting infrared signatures between the substituents and the phase changes that they induce. Herein, we report the infrared optical responses of three undoped hafnium oxide films where annealing conditions have been used to create films consisting primarily of the ferroelectric polar orthorhombic Pca21, antipolar orthorhombic Pbca, and monoclinic P21/c phases, as was confirmed via transmission electron microscopy (TEM), UV-visible optical properties, and electrical property measurements. Vibrational signatures acquired from synchrotron nano-Fourier transform infrared spectroscopy (nano-FTIR) are shown to be capable of differentiating between the phases in a nondestructive, rapid, and nanoscale manner. The utility of nano-FTIR is illustrated for a film exhibiting an antiferroelectric polarization response. In this sample, it is proven that this behavior results from the Pbca phase rather than the often-cited tetragonal phase. By demonstrating that IR spectroscopy can unambiguously distinguish phases in this material, this work establishes a tool needed to isolate the factors dictating the ferroelectric phase stability in HfO2-based materials.

Research Progress on the Application of Topological Phase Transition Materials in the Field of Memristor and Neuromorphic Computing.

Topological phase transition materials have strong coupling between their charge, spin orbitals, and lattice structure, which makes them have good electrical and magnetic properties, leading to promising applications in the fields of memristive devices. The smaller Gibbs free energy difference between the topological phases, the stable oxygen vacancy ordered structure, and the reversible topological phase transition promote the memristive effect, which is more conducive to its application in information storage, information processing, information calculation, and other related fields. In particular, extracting the current resistance or conductance of the two-terminal memristor to convert to the weight of the synapse in the neural network can simulate the behavior of biological synapses in their structure and function. In addition, in order to improve the performance of memristors and better apply them to neuromorphic computing, methods such as ion doping, electrode selection, interface modulation, and preparation process control have been demonstrated in memristors based on topological phase transition materials. At present, it is considered an effective method to obtain a unique resistive switching behavior by improving the process of preparing functional layers, regulating the crystal phase of topological phase transition materials, and constructing interface barrier-dependent devices. In this review, we systematically expound the resistance switching mechanism, resistance switching performance regulation, and neuromorphic computing of topological phase transition memristors, and provide some suggestions for the challenges faced by the development of the next generation of non-volatile memory and brain-like neuromorphic devices based on topological phase transition materials.

Building Block-Inspired Hybrid Perovskite Derivatives for Ferroelectric Channel Layers with Gate-Tunable Memory Behavior.

Ferroelectric photovoltaics driven by spontaneous polarization (Ps ) holds a promise for creating the next-generation optoelectronics, spintronics and non-volatile memories. However, photoactive ferroelectrics are quite scarce in single homogeneous phase, owing to the severe Ps fatigue caused by leakage current of photoexcited carriers. Here, through combining inorganic and organic components as building blocks, we constructed a series of ferroelectric semiconductors of 2D hybrid perovskites, (HA)2 (MA)n-1 Pbn Br3n+1 (n=1-5; HA=hexylamine and MA=methylamine). It is intriguing that their Curie temperatures are greatly enhanced by reducing the thickness of inorganic frameworks from MAPbBr3 (n=∞, Tc =239 K) to n=2 (Tc =310 K, ΔT=71 K). Especially, on account of the coupling of room-temperature ferroelectricity (Ps ≈1.5 μC/cm2 ) and photoconductivity, n=3 crystal wafer was integrated as channel field effect transistor that shows excellent a large short-circuit photocurrent ≈19.74 μA/cm2 . Such giant photocurrents can be modulated through manipulating gate voltage in a wide range (±60 V), exhibiting gate-tunable memory behaviors of three current states ("-1/0/1" states). We believe that this work sheds light on further exploration of ferroelectric materials toward new non-volatile memory devices.

Double-floating-gate memory device based on energy band engineered van der Waals heterostructure

Floating-gate memory devices based on two-dimensional van der Waals heterostructures are considered as promising candidates for next-generation nonvolatile memories. Here, we report a nonvolatile double-floating-gate (DFG) memory device based on a ReS2/boron nitride/black phosphorus (BP)/boron nitride/graphene heterostructure. By comparing with a single-floating-gate device we fabricated, the device shows enlarged memory window, high on–off ratio, and improved retention performance. Based on these findings, we propose energy band diagrams showing how the memory performance can be improved by energy band engineering through designing the van der Waals heterostructure. In the DFG structure, electrons could transfer between the ReS2 channel and BP as well as between BP and graphene, providing greater controllability for electron tunneling and injection. By choosing graphene and BP as two floating gates, an energy barrier rising from the conduction-band offset between multilayer graphene and BP is set up to efficiently prevent charge leakage from the graphene floating gate and, thus, improve the memory performance. Our work demonstrates an effective way for future designs of high-performance nonvolatile flash memories.

Revelation of resistive switching mechanism in AlOx based RRAM device

Resistive random access memory (RRAM) device based on conductive filaments (CF) is a promising candidate for next-generation nonvolatile memory applications. A detailed understanding of the resistive switching phenomenon is very important for RRAM development. In this paper, a numerical physics-based drift/diffusion model is presented to examine the resistive switching characteristic and morphological evolution of CF channels in AlOx based RRAM device. The experiment phenomenon and simulated results suggest that CF channels formed in the oxide film are composed of Cu metal and oxygen vacancy.

Quantum Confinement and Electronic Structure at the Surface of van der Waals Ferroelectric α-In2Se3.

Two-dimensional (2D) ferroelectric (FE) materials are promising compounds for next-generation nonvolatile memories due to their low energy consumption and high endurance. Among them, α-In2Se3 has drawn particular attention due to its in- and out-of-plane ferroelectricity, whose robustness has been demonstrated down to the monolayer limit. This is a relatively uncommon behavior since most bulk FE materials lose their ferroelectric character at the 2D limit due to the depolarization field. Using angle resolved photoemission spectroscopy (ARPES), we unveil another unusual 2D phenomenon appearing in 2H α-In2Se3 single crystals, the occurrence of a highly metallic two-dimensional electron gas (2DEG) at the surface of vacuum-cleaved crystals. This 2DEG exhibits two confined states, which correspond to an electron density of approximately 1013 electrons/cm2, also confirmed by thermoelectric measurements. Combination of ARPES and density functional theory (DFT) calculations reveals a direct band gap of energy equal to 1.3 ± 0.1 eV, with the bottom of the conduction band localized at the center of the Brillouin zone, just below the Fermi level. Such strong n-type doping further supports the quantum confinement of electrons and the formation of the 2DEG.

Stacked NbOx-based selector and ZrOx-based resistive memory for high-density crossbar array applications

Resistive random-access memory (RRAM) is a promising candidate for next-generation nonvolatile memory (NVM). Furthermore, RRAM is highly suitable for integration as a crossbar array (CBA). An RRAM-based CBA (R-CBA) shows various promising features in the fields of in-memory and neuromorphic computing. However, sneak-path current through unselected cells is a major obstacle in large-scale R-CBA development. To solve this issue, we propose a TiN/ZrOx/NbOx/Pt one selector-one resistor (1S1R) device structure that integrates the resistive switching and selector layer in a single stack. Material and electrical analyses were conducted to investigate the selector and resistive switching characteristics of the proposed device. The 1S1R device showed high selectivity (>5 × 101), low-resistance state/high-resistance state ratio (>5 × 101), long retention (>104 s), fast switching speeds (791 ns), stable operation, and excellent cell-by-cell variation. The conduction mechanism of the device was confirmed to be Schottky emission conduction. The maximum CBA size (139 × 139) was also obtained by calculating the read voltage margin. The proposed 1S1R device is suitable for large-scale CBA implementation and next-generation NVM.

Two-dimensional growth of Cu-based materials with a nonvolatile resistive switching behavior

Two-dimensional (2D) crystals have attracted much attention to the application in next-generation non-volatile memories due to their interesting structures and features. Herein, we report the controllable synthesis of 2D Cu2SxSe1– x crystals via a facile ambient pressure vapor deposition method. And the planar and vertical devices on the synthesized Cu2SxSe1– x crystals demonstrate a stable nonvolatile resistance switching. Most importantly, the planar Cu2SxSe1–x devices show a bipolar resistance switching behavior with a memory window of ∼103 and a relatively low operating voltage (<1 V). While the vertical Cu2SxSe1–x device exhibits a unipolar switching behavior with a large memory window of ∼105. Our findings in this work broaden the horizon for the in-situ synthesis of 2D materials and enlighten the possibility of related applications in neural synapse and artificial intelligence.