电荷俘获存储器中俘获层的研究进展

随着45nm和32nm技术节点的来临,传统Si3N4作为电荷俘获存储器的俘获层已经使器件的性能受到了限制。指出采用高k材料代替Si3N4作为俘获层已成为目前微电子材料研究的热点和趋势;着重对电荷俘获存储器的俘获层,包括对Si3N4掺O的无定形氧氮化硅(α-SiOxNy)俘获层、高k介质材料俘获层、植入纳米晶材料的俘获层及其叠层结构的研究现状和存在的问题进行了综述和分析,并对其进一步的研究趋势进行了展望。     

电荷俘获存储器阻挡层研究进展

随着非挥发性存储器(NVM)存储单元的特征尺寸进入20 nm节点,使用单层SiO2作为阻挡层的传统电荷俘获存储器结构性能上逐渐受到限制。基于阻挡层在存储器栅堆栈中的作用与基本要求,首先,指出单层SiO2作为阻挡层存在的主要问题,然后对高介电常数材料作为阻挡层时,其禁带宽度、介电常数、内部的缺陷密度以及退火工艺等方面对存储特性的影响进行了分析,同时对近年来研究较多的阻挡层能带工程进行了详细介绍,如SiO2和Al2O3的复合阻挡层结构、多层高介电常数材料的阻挡层结构等。最后,对目前研究进展中存在的问题以及未来的研究方向和趋势进行了总结和展望。     

An Ultrafast Nonvolatile Memory with Low Operation Voltage for High-Speed and Low-Power Applications

Memory plays a vital role in modern information society. High-speed and low-power nonvolatile memory is urgently demanded in the era of big data. However, ultrafast nonvolatile memory with nanosecond-timescale operation speed and long-term retention is still unavailable. Herein, an ultrafast nonvolatile memory based on van der Waals heterostructure is proposed, where a charge-trapping material, graphdiyne (GDY), serves as the charge-trapping layer. With the band-engineered heterostructure and excellent charge-trapping capability of GDY, charges are directly injected into the GDY layer and are persistently captured by the trapping sites in GDY, which result in an ultrafast writing speed (8 ns), a low operation voltage (30 mV), and a long retention time (over 10⁴ s). Moreover, a high on/off ratio of 10⁶ is demonstrated by this memory, which enables the achievement of multibit storage with 6 discrete storage levels. This device fills the blank of ultrafast nonvolatile memory technology, which makes it a promising candidate for next-generation high-speed and low-power-consumption nonvolatile memory.     

2D TMD Channel Transistors with ZnO Nanowire Gate for Extended Nonvolatile Memory Applications

2D transition metal dichalcogenides (TMDs) have been extensively studied due to their excellent physical properties. Mixed dimensional devices including 2D materials have also been studied, motivated by the possibility of any synergy effect from unique structures. However, only few such studies have been conducted. Here, semiconducting 1D ZnO nanowires are used as thin gate material to support 2D TMD field effect transistors (FETs) and 2D stack‐based interface trap nonvolatile memory. For the trap memory, deep level electron traps formed at the first MoS₂/second MoS₂ stack interface are exploited, since the first MoS₂ is treated in an atomic layer deposition chamber for a short while. On the one hand, a complementary inverter type memory device can also be achieved using a long single ZnO wire as a common gate to simultaneously support both n‐ and p‐channel TMD FETs. In addition, it is found that the semiconducting ZnO nanowire itself operates as an n‐type channel when the TMD materials can become a top‐gate to charge the ZnO channel. It means that 2D (bottom gated) and 1D channel (top gated) FETs are respectively operational in a single device structure. The 1D–2D mixed devices seem deserving broad attention in both aspects of novelty and functionality.     

Liquid‐Exfoliated Black Phosphorous Nanosheet Thin Films for Flexible Resistive Random Access Memory Applications

Black phosphorous (BP) is a unique layered p‐type semiconducting material. The successful use of BP nanosheets in field‐effect transistors fueled research on BP atomic layers that focuses on, e.g., the exploration of their optical and electronic properties, and promising applications in (opto)electronics. However, BP films are prone to degradation in ambient conditions, which prevents their commercial application. Here, a route to the application of BP films as an environmental stable nonvolatile resistive random access memory is presented. The BP films, which are prepared from exfoliated BP nanosheets in selected solvents, show solvent‐dependent degradation upon ambient exposure, inducing the formation of an amorphous top degraded layer (TDL). The TDL acts as an insulating barrier just below the Al electrode. This property that was only obtained by degradation, confers a bipolar resistive switching behavior with a high ON/OFF current ratio up to ~3 × 10⁵ and excellent retention ability over 10⁵ s to the flexible BP memory devices. The TDL also prevents propagation of degradation further into the film, ensuring excellent memory performance even after three month of ambient exposure.     

铁电存储场效应晶体管I-V特性的物理机制模拟

文章讨论的模型主要描述了铁电存储场效应晶体管（FEMFET）的I-V特性。从理论结果可反映出几何尺寸效应和材料参数对晶体管电特性的影响。传统的阈值电压的概念巳不再适用，由于铁电层反偏偶极子的开关作用，自发极化的增加对存储器的工作状态产生很小的影响。该模型可用于设计和工艺参数的优化，并由直观原型的方法得到了验证。     

Low‐Power Nonvolatile Charge Storage Memory Based on MoS2 and an Ultrathin Polymer Tunneling Dielectric

Low‐power, nonvolatile memory is an essential electronic component to store and process the unprecedented data flood arising from the oncoming Internet of Things era. Molybdenum disulfide (MoS₂) is a 2D material that is increasingly regarded as a promising semiconductor material in electronic device applications because of its unique physical characteristics. However, dielectric formation of an ultrathin low‐k tunneling on the dangling bond‐free surface of MoS₂ is a challenging task. Here, MoS₂‐based low‐power nonvolatile charge storage memory devices are reported with a poly(1,3,5‐trimethyl‐1,3,5‐trivinyl cyclotrisiloxane) (pV3D3) tunneling dielectric layer formed via a solvent‐free initiated chemical vapor deposition (iCVD) process. The surface‐growing polymerization and low‐temperature nature of the iCVD process enable the conformal growing of low‐k (≈2.2) pV3D3 insulating films on MoS₂. The fabricated memory devices exhibit a tunable memory window with high on/off ratio (≈10⁶), excellent retention times of 10⁵ s with an extrapolated time of possibly years, and an excellent cycling endurance of more than 10³ cycles, which are much higher than those reported previously for MoS₂‐based memory devices. By leveraging the inherent flexibility of both MoS₂ and polymer dielectric films, this research presents an important milestone in the development of low‐power flexible nonvolatile memory devices.     

Nonvolatile Floating‐Gate Memories Based on Stacked Black Phosphorus–Boron Nitride–MoS2 Heterostructures

Research on van der Waals heterostructures based on stacked 2D atomic crystals is intense due to their prominent properties and potential applications for flexible transparent electronics and optoelectronics. Here, nonvolatile memory devices based on floating‐gate field‐effect transistors that are stacked with 2D materials are reported, where few‐layer black phosphorus acts as channel layer, hexagonal boron nitride as tunnel barrier layer, and MoS₂ as charge trapping layer. Because of the ambipolar behavior of black phosphorus, electrons and holes can be stored in the MoS₂ charge trapping layer. The heterostructures exhibit remarkable erase/program ratio and endurance performance, and can be developed for high‐performance type‐switching memories and reconfigurable inverter logic circuits, indicating that it is promising for application in memory devices completely based on 2D atomic crystals.     

Small‐Molecule‐Based Organic Field‐Effect Transistor for Nonvolatile Memory and Artificial Synapse

With the incorporation of tailorable organic electronic materials as channel and storage materials, organic field‐effect transistor (OFET)‐based memory has become one of the most promising data storage technologies for hosting a variety of emerging memory applications, such as sensory memory, storage memory, and neuromorphic computing. Here, the recent state‐of‐the‐art progresses in the use of small molecules for OFET nonvolatile memory and artificial synapses are comprehensively reviewed, focusing on the characteristic features of small molecules in versatile functional roles (channel, storage, modifier, and dopant). Techniques for optimizing the storage capacity, speed, and reliability of nonvolatile memory devices are addressed in detail. Insight into the use of small molecules in artificial synapses constructed on OFET memory is also obtained in this emerging field. Finally, the strategies of molecular design for improving memory performance in view of small molecules as storage mediums are discussed systematically, and challenges are addressed to shed light on the future development of this vital research field.     

2D/2D Heterojunction of Ultrathin MXene/Bi2WO6 Nanosheets for Improved Photocatalytic CO2 Reduction

Exploring cheap and efficient cocatalysts for enhancing the performance of photocatalysts is a challenge in the energy conversion field. Herein, 2D ultrathin Ti₃C₂ nanosheets, a kind of MXenes, are prepared by etching Ti₃AlC₂ with subsequent ultrasonic exfoliation. A novel 2D/2D heterojunction of ultrathin Ti₃C₂/Bi₂WO₆ nanosheets is then successfully prepared by in situ growth of Bi₂WO₆ ultrathin nanosheets on the surface of these Ti₃C₂ ultrathin nanosheets. The resultant Ti₃C₂/Bi₂WO₆ hybrids exhibit a short charge transport distance and a large interface contact area, assuring excellent bulk‐to‐surface and interfacial charge transfer abilities. Meanwhile, the improved specific surface area and pore structure endow Ti₃C₂/Bi₂WO₆ hybrids with an enhanced CO₂ adsorption capability. As a result, the 2D/2D heterojunction of ultrathin Ti₃C₂/Bi₂WO₆ nanosheets shows significant improvement on the performance of photocatalytic CO₂ reduction under simulated solar irradiation. The total yield of CH₄ and CH₃OH obtained on the optimized Ti₃C₂/Bi₂WO₆ hybrid is 4.6 times that obtained on pristine Bi₂WO₆ ultrathin nanosheets. This work provides a new protocol for constructing 2D/2D photocatalytic systems and demonstrates Ti₃C₂ as a promising and cheap cocatalyst.     

Ice‐Assisted Synthesis of Black Phosphorus Nanosheets as a Metal‐Free Photocatalyst: 2D/2D Heterostructure for Broadband H2 Evolution

A 2D/2D heterojunction of black phosphorous (BP)/graphitic carbon nitride (g‐C₃N₄) is designed and synthesized for photocatalytic H₂ evolution. The ice‐assisted exfoliation method developed herein for preparing BP nanosheets from bulk BP, leads to high yield of few‐layer BP nanosheets (≈6 layers on average) with large lateral size at reduced duration and power for liquid exfoliation. The combination of BP with g‐C₃N₄ protects BP from oxidation and contributes to enhanced activity both under λ > 420 nm and λ > 475 nm light irradiation and to long‐term stability. The H₂ production rate of BP/g‐C₃N₄ (384.17 µmol g^?1 h^?1) is comparable to, and even surpasses that of the previously reported, precious metal‐loaded photocatalyst under λ > 420 nm light. The efficient charge transfer between BP and g‐C₃N₄ (likely due to formed N? P bonds) and broadened photon absorption (supported both experimentally and theoretically) contribute to the excellent photocatalytic performance. The possible mechanisms of H₂ evolution under various forms of light irradiation is unveiled. This work presents a novel, facile method to prepare 2D nanomaterials and provides a successful paradigm for the design of metal‐free photocatalysts with improved charge‐carrier dynamics for renewable energy conversion.     

Reconfigurable Logic‐in‐Memory and Multilingual Artificial Synapses Based on 2D Heterostructures

Nonvolatile logic devices have attracted intensive research attentions recently for energy efficiency computing, where data computing and storage can be realized in the same device structure. Various approaches have been adopted to build such devices; however, the functionality and versatility are still very limited. Here, 2D van der Waals heterostructures based on direct bandgap materials black phosphorus and rhenium disulfide for the nonvolatile ternary logic operations is demonstrated for the first time with the ultrathin oxide layer from the black phosphorus serving as the charge trapping as well as band‐to‐band tunneling layer. Furthermore, an artificial electronic synapse based on this heterostructure is demonstrated to mimic trilingual synaptic response by changing the input base voltage. Besides, artificial neural network simulation based on the electronic synaptic arrays using the handwritten digits data sets demonstrates a high recognition accuracy of 91.3%. This work provides a path toward realizing multifunctional nonvolatile logic‐in‐memory applications based on novel 2D heterostructures.     

Nonvolatile Random Access Memory and Energy Storage Based on Antiferroelectric Like Hysteresis in ZrO2

To date antiferroelectrics have not been considered as nonvolatile memory elements because a removal of the external field causes a depolarization, resulting in a loss of the stored information. In comparison to ferroelectrics, antiferroelectrics are known for their enhanced fatigue resistance. Therefore, the main scope of this study is the development of a new memory device concept that would enable the usage of antiferroelectrics as a nonvolatile material with improved wake‐up and enhanced endurance properties. Recent studies have shown antiferroelectric behavior in ZrO₂, a material that is widely used in semiconductor industry, especially in dynamic random access memories. The basis of the new concept is the antiferroelectric hysteresis combined with the use of different workfunction electrodes that induce an internal bias field. Utilizing this approach, the field cycling endurance is drastically improved. Combining a comprehensive material study and electrical trap spectroscopy together with Landau–Ginzburg–Devonshire formalism, a proof of concept for a novel antiferroelectric random access memory is presented. For implementing a nonvolatile random access memory, the capacitors have to be realized in a 3D integrated version. These 3D integrated ZrO₂ capacitors can be used as energy storage devices as well, showing record high energy storage density and very high energy efficiency values.     

2D Metal–Organic Framework Nanosheets with Time‐Dependent and Multilevel Memristive Switching

Metal–organic framework (MOF) nanosheets have attracted significant interests for sensing, electrochemical, and catalytic applications. Most significantly, 2D MOF with highly accessible sites on the surface is expected to be applicable in data storage. Here, the memory device is first demonstrated by employing M‐TCPP (TCPP: tetrakis(4‐carboxyphenyl)porphyrin, M: metal) as resistive switching (RS) layer. The as‐fabricated resistive random access memory (RRAM) devices exhibit a typical electroforming free bipolar switching characteristic with on/off ratio of 10³, superior retention, and reliability performance. Furthermore, the time‐dependent RS behaviors under constant voltage stress of 2D M‐TCPP–based RRAMs are systematically investigated. The properties of the percolated conducting paths are revealed by the Weibull distribution by collecting the measured turn‐on time. The multilevel information storage state can be gotten by setting a series of compliance current. The charge trapping assisted hopping is proposed as operation principle of the MOF‐based RRAMs which is further confirmed by atomic force microscopy at electrical modes. The research is highly relevant for practical operation of 2D MOF nanosheet–based RRAM, since the time widths, magnitudes of pulses, and multilevel‐data storage can be potentially set.     

Surface Charge Modification on 2D Nanofluidic Membrane for Regulating Ion Transport

2D nanofluidic membranes are capable of regulating ion transport toward various applications concerning energy and environment, which is primarily contributed by the excess charge on the interior surface of narrow nanoscale pores. However, there is still a lack of comprehensive summaries and discussions on the surface charge modification principles and strategies of 2D nanofluidic membranes, as well as the practical applications of charge-modified 2D nanofluidic membranes for regulating ion transport. In this review, the surface charge modification principles and charge modification methods of 2D nanofluidic membranes are first introduced in detail, which is of great significance for improving the ion regulation capability of membranes and realizing the design of nanochannel materials. Next, recent advances in the two typical applications of concentration cells and water treatment based on charge-modified 2D nanofluidic membranes are summarized. Finally, some challenges and prospects related to charge-modified 2D nanofluidic membranes are discussed to indicate directions for future research in this field. It is anticipated that this review will provide valuable strategies for the development of high-performance charge-modified 2D nanofluidic membranes toward energy and environment applications.     

矢量基二维DCT修剪在DSP上的内存存取减少方法

本文针对矢量基二维DCT修剪提出内存存取减少方法.该方法旨在减少计算中因权重因子和信号输入而导致的内存存取.它首先利用权重因子的属性将计算流程图内每相邻两阶段内的蝴蝶运算单元进行融合,然后再以较少的权重因子来计算.本文采用通用DSP处理器来验证该方法对矢量基二维DCT修剪算法的有效性.并且实验结果显示该方法相比于常规方法可以大幅度减少运算所需的时钟周期数、降低对运算中对内存的存取量、以及占用更少的内存.     

D2D网络中信道选择与功率控制策略研究

针对D2D通信的资源分配问题,该文研究了D2D信道选择与功率控制策略。在保证蜂窝用户服务质量(QoS)的前提下,提出一种基于启发式的D2D信道选择算法,为系统内的D2D用户找到合适的信道复用资源。同时,利用拉格朗日对偶方法求解得到D2D用户最优传输功率。仿真结果表明当蜂窝用户与多对D2D用户共享信道资源时能够大幅度提升系统平均吞吐量。在相同条件下,该算法的性能要明显优于现有算法。     

4D Printed Shape Memory Anastomosis Ring with Controllable Shape Transformation and Degradation

Biofragmentable anastomosis ring (BAR) is an ideal sutureless alternative for intestinal connection that is frequently demanded in colonic surgery. However, it is challenging to insert a bulky BAR into the soft and slippery intestine. Here 4D printing of an anastomosis ring with shape memory capability is presented via fused deposition modeling (FDM) 3D printing. The shape memory anastomosis ring can recover from a compressed shape that facilitates the insertion to the permanent shape for connection and supporting. Degradation kinetics is tuned by controlling the blending composition of polylactic acid and poly(lactic-co-glycolic acid), so that the device can be excreted after the intestine healing. The shape recovery temperature is adjusted to 50 °C that the human body can withstand for a while. Grid structure and hook lock are designed and printed to guarantee dimension reduction upon programming and stable connection after shape recovery, respectively. A conceptual anastomotic operation shows the advantages and prospects of shape transformation. The 4D printing strategy may promote intestinal anastomosis development and inspire more opportunities for minimally invasive medical surgery.     

面向蜂窝网络的D2D多播通信的分簇和中继选择方法

传统蜂窝网络中,信道衰减的随机性和不确定性导致小区边缘用户的接收性能很差,尤其是面向视频传输等速率要求较高时其弊端更加凸显。D2D通信因其配置灵活性可作为传统蜂窝网络架构的有利补充,能有效改善边缘用户的性能。该文针对D2D通信的多播传输,分析了系统最小时延成本下的中继数量和分簇算法,提出一种基于分簇和中继选择的低时延D2D多播方案。该方案可以自适应选择多播重传中的中继的数量和中继节点到基站的距离,同时给出最优的带宽资源分配机制。仿真结果表明,与其他方案相比,所提方法能有效减少系统时延,提高边缘用户体验和系统性能。