Search

Two-dimensional (2D) van der Waals (vdW) heterostructures with spontaneous intrinsic ferroelectrics play an essential role in ferroelectric memories. Also, the reversal of polarized directions induces band alignment transitions among different types to provide a new path for multifunctional devices. In this work, the structural and electronic properties of 2D VS2/Ga2O3 vdW heterostructures under different polarizations were investigated using first-principles calculations with the vdW correction of the DFT-D2 method. The results reveal that the polarized direction of a 2D Ga2O3 monolayer can cause a distinct band structure reversion from a metal to a semiconductor due to the shift of band alignment induced by the interlayer charge transfer. Moreover, the VS2/P↑ Ga2O3 heterostructures retain type-I and type-II band alignments in the majority and minority channel, respectively, under an external electric field. Interestingly, applying the external electric field for VS2/P↓ Ga2O3 heterostructures can lead to a transition from type-II to type-I in the majority channel, and from type-II to type-III in the minority channel. Our work provides a feasible way to realize 2D VS2/Ga2O3 vdW heterostructures for potential applications in ferroelectric memories and electrostatic gating dependent multiple band alignment devices. [ABSTRACT FROM AUTHOR]

A memristor‐based reinforcement learning (RL) system has shown outstanding performance in achieving efficient autonomous decision‐making and edge computing. Sarsa (λ) is a classical multistep RL algorithm that records state with λ decay and guides policy updates, significantly improving the algorithm convergence speed. However, λ decay implementation of traditional computing hardware is confined by the extensive computation of power exponential decay. Herein, the value update equation for Sarsa (λ) is implemented by using the topological structure of the memristor array, without complex circuits. Where, most importantly, the critical λ decay function is realized by a TiOx‐based memristor with conductance decay property. The energy required for floating‐point operations can be significantly reduced while accelerating the convergence speed. Then, a path planning task is demonstrated based on intrinsic conductance decay property and shows outstanding performance. Finally, the information of rounds used for the task is obtained, which is based on the intrinsic decay property of the TiOx‐based memristor, maps into a 32 × 32 memristor array in parallel to calculate the value of each round. The results indicate that the experimental data have similar results to the simulations. Herein, thus, it provides a hardware‐enabled scheme for the memristor‐based RL algorithm implementation. [ABSTRACT FROM AUTHOR]

In this study, a NbO2-based selector was designed that can change high resistance states to low resistance states due to the insulator–metal transition (IMT). A one-selector-one-resistor cell for a 3D crossbar array composed of this selector and a TiN/TiO2/TiN bipolar resistive random access memory (RRAM) in series was modeled using the COMSOL finite element multiphysics software package. First, the temperature dependencies of the electrical conductivity (σ), thermal conductivity (kth), and mass specific heat (CP) were used to compare two IMT selectors, which showed that the NbO2-based selector better matched the RRAM due to its appropriate hysteresis width (hw), threshold voltage (Vth), and low off-state current (Ioff). Second, the effect of size variations for the NbO2 on the electrical performance of the IMT selector was investigated. Vth, hold voltage (Vhold), threshold current (Ith), Ioff, and Ith/Ioff ratio of the IMT selector were sensitive to thickness (L) and filament radius (r) of NbO2. L and r were designed by comparing the electrical characteristics of the NbO2 selectors of different sizes to make a connection with the TiO2-based bipolar RRAM. Finally, a TiN/NbO2/TiN/TiO2/TiN stack structure was simulated, and the results show a significantly reduced leakage current (1 μA), high read window (15.8), and improved readout margin (>27 word lines), which are suitable for next-generation high-density memory devices. This study provides guidance for the design of selectors connected to the RRAM, which is beneficial for circuit designs and process manufacturing. [ABSTRACT FROM AUTHOR]

The effect of interfacial fluorination on the structure, electronic properties, and performance of the HfO2/Al2O3 interface in charge-trapping memory (CTM) devices is investigated using the first-principles calculation. The impact of the interface states on the characteristics of traps in the HfO2 trapping layer at the HfO2/Al2O3 interface is studied first, and the results indicate that the interfacial states lead to performance degradation with respect to both reliability and the memory window of CTM devices during program/erase cycles. In the study of F passivation, F substitutions (FO) and F interstitials (Fi) tend to improve the thermal stability of the interface for higher interfacial F contents. Further, the FO-passivated interface is energetically more stable than the Fi-passivated interface. In addition, the FO-passivated interface can reduce the interface states that are partially (or completely) caused by breaking covalent interfacial bonds. Furthermore, a substantially improved HfO2/Al2O3 interface, with effective interfacial passivation in CTM devices, is obtained. Therefore, this study helps explain the intrinsic principle of interface passivation and opens new ways for performance improvement of the HfO2/Al2O3 interface in CTM devices. [ABSTRACT FROM AUTHOR]

In this work, a compact model of the diffusive memristor is proposed from the perspective of the transition of electronic transmission mechanisms induced by the dynamics of the filament. First, a new physical model is established based on tunneling mechanisms that are used to fit the experimental data, and the results indicate that it is versatile enough for various diffusive memristors. In addition, the threshold voltage (V th) of the diffusive memristor negatively correlates with the ratio of ionic migration and the diffusion coefficient (u i /Ds), and the hold voltage (V h) positively correlates with the ratio of ionic diffusion and the migration coefficient (Ds/u i), which is useful for the selection of materials to achieve target electrical properties. Furthermore, the different parameters that influence the simulated switching curve are explored. The results indicate that the desired electrical characteristics can be obtained by adjusting these parameters. A compact electrical module model is then built and tested in LTspice to carry out bio-neuron and bio-synaptic performances completely. These simulations demonstrate that the model is reliable for exploring diffusive memristor applications. [ABSTRACT FROM AUTHOR]

Herein, an improved memristor model with a controllable forgetting rate due to ion diffusion is proposed. A synaptic learning circuit based on this model is simulated with PSpice to complete synaptic bionics. First, the pulse pair superposition method, which is consistent with biological phenomena, is used to verify spike timing‐dependent plasticity (STDP); this proves that the modified model simulates biological synaptic behavior. Second, a habituation circuit constructed from a memristor and an analog behavioral modeling (ABM) device is designed to realize nonassociative learning. Finally, a new circuit with the improved model is built for Pavlov's associative memory implementation, simplifying the complexity of the circuit. The improved model can better realize the basic learning and memory modes of organisms and thus provide more brain‐inspired computing options. [ABSTRACT FROM AUTHOR]

In this work, a graphene (GR)/MoS2/GR selector was proposed based on first principle calculations. First, MoS2 was chosen as the resistive switching layer due to its high carrier mobility and was doped with nine kinds of dopants. Semiconductor characteristics were still maintained with P, Si, and Ti doping, while the others showed semimetallic properties. Then, heterostructures were built between metal GR and MoS·X (X = S, P, Si, Ti), and the conductivities of MoS·Si and MoS·Ti were obviously improved with the GR electrode through analysis of the impurity orbital contribution to the band energy. The plane average electrostatic potential and the charge density difference show that the Schottky barrier height and width of the GR/MoS·Si interface were the smallest and that the intensity of the built-in electric field was better than that of GR/MoS2 and GR/MoS·Ti. Finally, GR/MoS·X(X = S, Si, Ti)/GR selectors were proposed, and the electronic transmission shows that the ON-state current (Ion) and nonlinear coefficient of the GR/MoS·Si/GR selector were increased by two and three orders of magnitude, respectively, and the threshold voltage (Vth) was reduced by approximately 1 V, which can better suppress the leakage current in a one-selector one-RRAM cross array. This work may be instructive and valuable for the design and optimization of GR/MoS2/GR selectors. [ABSTRACT FROM AUTHOR]

Blue phosphorene (BlueP) has been widely researched recently as a potential material for novel photocatalytic and electronic devices. In this letter, due to its similar in-plane hexagonal lattice structure to MoS2, BlueP/MoS2 van der Waals heterostructures were built in six configurations. The II-stacking configuration was the most stable due to the lowest binding energy obtained from the calculation results. Furthermore, by controlling the external vertical strain, the geometry structures were optimized and the electronic structures of the BlueP/MoS2 heterostructure were modulated. We found that when the interlayer distance was 3.71 Ĺ, the structure was the most optimized. In addition, as the result of charge transfer at the interlayer, a built-in electric field was formed in the BlueP/MoS2 heterostructure, which explained the formation of the type-II band alignment structure. The optical properties results show that the BlueP/MoS2 heterostructure has a wide optical response range and good light absorption ability, which indicated significant potential for BlueP/MoS2 heterostructure use in the next generation of photovoltaic devices and water-splitting materials. [ABSTRACT FROM AUTHOR]