Novel Conjugated Side Chain Fluorinated Polymers Based on Fluorene for Light-Emitting and Ternary Flash Memory Devices

Three novel conjugated polymers based on 9,9′-dioctylfluorene unit and isoindolo[2,1-a]benzimidazol-11-one with different fluorine substituents (0, 2 and 4) were synthesized. PLED and resistive memory devices based on these polymers were prepared consequently. PLED based on four-fluorinated polymer showed the highest maximum brightness of 3192 cd m⁻² with almost 5-fold increase of current efficiency 8-fold increase of external quantum efficiency compared to that of the other two, and all the PLEDs exhibited good emission stability with no noticeable change of electroluminescence even under high voltage of 10 V. The memory device of doubly-fluorinated polymer exhibited ternary flash behavior with threshold voltages below −2.5 V, while device of four-fluorinated polymer possessed ON/OFF current ratio above 10⁴. Impact of fluorine substitutions on the performance of devices were briefly investigated. The results revealed that the improvement of device performance might not scale with the increasing number of fluorine substitutions, and the four-fluorine-substituted polymer and doubly-fluorinated polymer could be encouraging materials for applications of PLED and resistive memory device and worth of further design of other new polymer systems.     

The redox of hydroxyl-assisted metallic filament induced resistive switching memory based on a biomaterial-constructed sustainable and environment-friendly device

Using biomaterial-constructed resistive switching memory devices has attracted great attention for the potential application in advanced electronic components because of their variety of advantages, such as low cost, sustainability, environment-friendly, and so on. In this work, after a series of treatments, an edible mushroom as an intermediate insulating material was assembled into an Ag/biofilm/metal structure, in which the metals such as Al, Cu, Ag, and Ti were chosen as the bottom electrode to explore in-depth physical mechanisms. The transmission mechanism of resistive switching memory behavior in an Ag/biofilm/metal device was studied in detail. It was found that the redox of hydroxyl-assisted Ag filaments could be easily formed on an inactive metal bottom electrode through the mushroom film by redox reaction under applied voltage. This work provides an ingenious potential application in wearable, flexible, sustainable, and environment-friendly biologically resistive random-access memories.     

Ternary Conductance Switching Realized by a Pillar[5]arene-Functionalized Two-Dimensional Imine Polymer Film

Nowadays, most manufacturing memory devices are based on materials with electrical bistability (i. e., “0” and “1”) in response to an applied electric field. Memory devices with multilevel states are highly desired so as to produce high-density and efficient memory devices. Herein, we report the first multichannel strategy to realize a ternary-state memristor. We make use of the intrinsic sub-nanometer channel of pillar[5]arene and nanometer channel of a two-dimensional imine polymer to construct an active layer with multilevel channels for ternary memory devices. Low threshold voltage, long retention time, clearly distinguishable resistance states, high ON/OFF ratio (OFF/ON1/ON2=1 : 10 : 10³), and high ternary yield (75 %) were obtained. In addition, the flexible memory device based on 2DP_TPAZ+TAPB can maintain its stable ternary memory performance after being bent 500 times. The device also exhibits excellent thermal stability and can tolerate a temperature as high as 300 °C. It is envisioned that the results of this work will open up possibilities for multistate, flexible resistive memories with good thermal stability and low energy consumption, and broaden the application of pillar[n]arene.     

新型Ti3C2 MXene的化学制备及基于MXene忆阻器特性与机理

阻变器件是一种微电子器件,具有阻值可在两个甚至两个以上的阻态之间重复变化的特点。忆阻器作为新型的阻变器件,具有可连续变化的丰富阻态。近年来因其具备简单的二端结构、高集成度以及低工作电压等特性,在新型非易失性存储以及构建神经形态系统等方面被广泛研究。但其在实现应用的过程中仍存在着稳定性较差等问题。近期一些工作证明了二维材料如氧化石墨烯在优化忆阻器性能方面具备良好的应用潜力。MXene是一种具备类似石墨烯结构的新型二维过渡金属碳/氮化物,因其具备二维层状结构显现出特殊的力学以及电学特性,有望应用于忆阻器中以提高器件的电学性能。在本文中,我们通过化学湿法刻蚀制备了Ti₃C₂粉末,通过旋涂工艺在忆阻器结构中引入Ti₃C₂薄膜。Ti₃C₂ MXene与SiO₂同时作为忆阻器阻变层,制备了Cu/Ti₃C₂/SiO₂/W结构的忆阻器,并且对其相关电学特性进行了探究。在该器件上,通过实验测得忆阻器典型的开关特性曲线并在双向直流电压下针对高、低阻态的可重复性、稳定性进行了实验。结果表明该器件能够在100个扫描循环过程中保持稳定的高、低阻态达到10⁴ s以上。同时,该器件状态能够受脉冲电压调节,实现突触间典型的双脉冲易化行为。实验结果表明基于Ti₃C₂ MXene的忆阻器将有望应用于构建新兴存储设备以及人工神经形态系统。     

Cu12Sb4S13量子点的光照增强阻变性能

采用热注入法制备了粒径为7.9 nm的Cu₁₂Sb₄S₁₃量子点（CAS QDs）,并利用旋涂法在室温下制备了结构为FTO/CAS QDs/Au（其中FTO为导电玻璃）的阻变存储器（RRAM）.在光照条件下,该三明治结构的RRAM呈现典型的双极性阻变开关特征,具有-0.38 V/0.42 V的低工作电压和10⁵的高阻变开关比,并表现出优异的数据保持性和耐久性.在持续工作1.4×10⁶ s和经过10⁴次快速读取后,器件阻变性能变化率小于0.1%.在光照和电场共同作用下,S^2-导电通道的形成与破坏和FTO/CAS QDs界面肖特基势垒高度的调制是FTO/CAS QDs/Au在高阻态与低阻态之间转变的原因.     

Tunable Electronic Memory Performances Based on Poly(Triphenylamine) and Its Metal Complex via a SuFEx Click Reaction

A triphenylamine derivative decorated with an azobenzene group (TDA) was synthesized via a SuFEx click reaction and its polymer, poly(triphenylamine) (PTDA), was polymerized through a redox polymerization. More interestingly, its polymeric metal complex, PTDA‐Fe, can be simply obtained via one‐pot reaction between TDA and FeCl₃ owing to TDA showing a strong affinity to the Fe^III ion. The sandwich memory device based on PTDA nanofilms as active layers exhibited a binary memory performance. However, the memory device based on its polymeric metal complex exhibited a unique ternary memory behavior. The different memory performances should come from the different conductive mechanism. The mechanism of such ternary memory devices is illustrated based on both the theoretical calculation and experiments. Our work provides new insights into the preparation of novel materials for multilevel memory devices.     

Surface Engineering of ITO Substrates to Improve the Memory Performance of an Asymmetric Conjugated Molecule with a Side Chain

Organic multilevel random resistive access memory (RRAM) devices with an electrode/organic layer/electrode sandwich‐like structure suffer from poor reproducibility, such as low effective ternary device yields and a wide threshold voltage distribution, and improvements through organic material renovation are rather limited. In contrast, engineering of the electrode surfaces rather than molecule design has been demonstrated to boost the performance of organic electronics effectively. Herein, we introduce surface engineering into organic multilevel RRAMs to enhance their ternary memory performance. A new asymmetric conjugated molecule composed of phenothiazine and malononitrile with a side chain (PTZ‐PTZO‐CN) was fabricated in an indium tin oxide (ITO)/PTZ‐PTZO‐CN/Al sandwich‐like memory device. Modification of the ITO substrate with a phosphonic acid (PA) prior to device fabrication increased the ternary device yield (the ratio of effective ternary device) and narrowed the threshold voltage distribution. The crystallinity analysis revealed that PTZ‐PTZO‐CN grown on untreated ITO crystallized into two phases. After the surface engineering of ITO, this crystalline ambiguity was eliminated and a sole crystal phase was obtained that was the same as in the powder state. The unified crystal structure and improved grain mosaicity resulted in a lower threshold voltage and, therefore, a higher ternary device yield. Our result demonstrated that PA modification also improved the memory performance of an asymmetric conjugated molecule with a side chain.     

Cyclometalated Platinum(II) Complexes with Donor-Acceptor-Containing Bidentate Ligands and Their Application Studies as Organic Resistive Memories

A series of heteroleptic cyclometalated platinum(II) complexes, [Pt(C^N)(O^O)], ( 1 – 10 ) with various donors and acceptors has been synthesized and characterized by ¹H NMR spectroscopy, elemental analyses, infrared spectroscopy and mass spectrometry. The X-ray structure of 2 has also been determined. The electrochemical and photophysical properties of the platinum(II) complexes were studied. These experimental results have been supported by computational studies. Furthermore, two of the complexes have been employed as the active material in the fabrication of resistive memory devices, exhibiting stable binary memory performance with low operating voltage, high ON/OFF ratio and long retention time.     

The Old Polyoxometalates in New Application as Molecular Resistive Switching Memristors

The coming big-data era has created a huge demand for next-generation memory technologies with characters of higher data-storage densities, faster access speeds, lower power consumption and better environmental compatibility. In this field, the design of resistive switching active materials is pivotal but challengeable. Polyoxometalates (POMs) are promising candidates for next-generation molecular memristors due to their versatile redox characters, excellent electron reservoirs and good compatibility/convenience in microelectronics processing. In this review, five kinds of POM-based active materials in nonvolatile memories (inorganic POMs, crystalline organic-inorganic hybrid POMOFs, polymer modified POMs, POM/transition metal oxides composites and the deposition of POM on metal surfaces) were described. The components of POMs active materials, device fabrications, device parameters, and resistive switching mechanisms relative to their structures were summarized. Finally, challenges and future perspectives of POMs-based memristors were also presented.     

Opportunity of spinel ferrite materials in nonvolatile memory device applications based on their resistive switching performances

The opportunity of spinel ferrites in nonvolatile memory device applications has been demonstrated by the resistive switching performance characteristics of a Pt/NiFe(2)O(4)/Pt structure, such as low operating voltage, high device yield, long retention time (up to 10(5) s), and good endurance (up to 2.2 × 10(4) cycles). The dominant conduction mechanisms are Ohmic conduction in the low-resistance state and in the lower-voltage region of the high-resistance state and Schottky emission in the higher-voltage region of the high-resistance state. On the basis of measurements of the temperature dependence of the resistances and magnetic properties in different resistance states, we explain the physical mechanism of resistive switching of Pt/NiFe(2)O(4)/Pt devices using the model of formation and rupture of conducting filaments by considering the thermal effect of oxygen vacancies and changes in the valences of cations due to the redox effect.     

One-Step Fabrication of Bio-Compatible Coordination Complex Film on Diverse Substrates for Ternary Flexible Memory

Recently, resistance random access memories (RRAMs) have been studied extensively, because the demand for information storage is increasing. However, it remains challenging to obtain a flexible device because the active materials involved need to be nontoxic, nonpolluting, distortion-tolerable, and biodegradable as well adhesive to diverse flexible substrates. In this paper, tannic acid (TA) and an iron ion (Fe^III) coordination complex were employed as the active layer in a sandwich-like (Al/active layer/substrate) device to achieve memory performance. A nontoxic, biocompatible TA-Fe^III coordination complex was synthesized by a one-step self-assembly solution method. The retention time of the TA-Fe^III memory performance was up to 15 000 s, the yield up to 53 %. Furthermore, the TA-Fe^III coordination complex can form a high-quality film and shows stable ternary memory behavior on various flexible substrates, such as polyethylene terephthalate (PET), polyimide (PI), printer paper, and leaf. The device can be degraded by immersing it in vinegar solution. Our work will broaden the application of organic coordination complexes in flexible memory devices with diverse substrates.     

Amphiphilic Carbazole‐Containing Compounds with Lower Critical Solution Temperature Behavior for Supramolecular Self‐Assembly and Solution‐Processable Resistive Memories

The self‐organization and resistive memory performances of a series of newly synthesized water‐soluble amphiphilic carbazole derivatives have been explored. Temperature‐dependent UV/Vis absorption spectroscopy has been conducted to study the isodesmic self‐assembly mechanism of the carbazole‐containing compounds. This class of compounds also exhibits interesting lower critical solution temperature properties, which are sensitive to concentration and ionic additives. One of the compounds has been solution‐processed and utilized as an active material in the engineering of resistive memory devices, exhibiting a switching voltage of about 3.9 V, a constant ON/OFF current ratio of 10⁶, and a long retention time of 10⁴ s. The present work demonstrates the versatile potential applications of water‐soluble amphiphilic carbazole‐containing compounds in supramolecular chemistry and resistive memory devices.     

A review of transition metal chalcogenide/graphene nanocomposites for energy storage and conversion

Recent advances in the applications of transition metal chalcogenides/graphene (TMC/graphene) nanocomposites in future energy storage and conversion are reviewed. The synthesis processes and structures of TMC/graphene, workingpriciple of evergy energy device, and the electrochemical performances are summarized.     

Synthesis and characterization of metal-incorporated aniline formaldehyde resin modified by amino acid for antimicrobial applications

Advances in metal incorporated resins are now an active field of research. To develop resin having better antimicrobial and thermal activity, a series of metal-chelated resins have been synthesized by the condensation of (4-aminobenzene-1,3-diyl)dimethanol with 2,6-diaminohexanoic acid in alkaline medium and then this polymeric ligand further reacts with transition metal ions forming various coordination polymers. (4-Aminobenzene-1,3-diyl)dimethanol was initially prepared by the reaction of aniline and formaldehyde in 1?:?2 molar ratio in alkaline medium. The analytical data reveal that the polymer metal complexes of Mn(II), Co(II), and Ni(II) are coordinated with two water molecules, which are further supported by FTIR spectra and TGA data. Comparative analyses of the polymer metal complexes in thermal curves show better thermal stability than the polymeric ligand. Since these resins are relatively stable at high temperatures, they can be used for medical and biomaterial applications requiring thermal sterilization, solvent-resist coating materials because of their insoluble nature, and antifouling coating materials owing to antimicrobial activity in ?elds such as life-saving medical devices and the bottoms of ships.     

Memory devices based on lanthanide (Sm3+, Eu3+, Gd3+) complexes

Memory effects in single-layer organic light-emitting devices based on Sm3+, Gd3+, and Eu3+ rare earth complexes were realized. The device structure was indium-tin-oxide (ITO)/3,4-poly(ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT)/Poly(N-vinyl carbazole) (PVK): rare earth complex/LiF/Ca/Ag. It was found experimentally that all the devices exhibited two distinctive bistable conductivity states in current-voltage characteristics by applying negative starting voltage, and more than 10(6) write-read-erase-reread cycles were achieved without degradation. Our results indicate that the rare earth organic complexes are promising materials for high-density, low-cost memory application besides the potential application as organic light-emitting materials in display devices.     

Application of ion-in-conjugation molecules in resistive memories and gas sensors: The role of conjugation

Ion-in-conjugation(IIC) materials are eme rging as an important class of organic electronic materials with wide applications in energy storage,resistive memories and gas sensors.Many IIC materials were designed and investigated,however the role of conjugation in IIC materials' performance is yet investigated.Here we designed two molecules obtained by condensation of 4-butylaniline and oxocarbon acid.Squaric acid derivatives squaraine named SA-Bu and a croconamide named CA-Bu which only differ in their oxocarbon cores.While employing SA-Bu and CA-Bu as resistive memory and gas sensory materials,SA-Bu has attained promising performance in ternary memo ry and detection of NO_2 as low as 10 parts-per-billion whereas CA-Bu show mainly binary memory behavior and negligible NO_2 response.Theoretical calculations reveal that conjugation of CA-Bu was distorted by the increased steric hindrance,frustrating the charge transport and suppressing the conductivity.Our work demonstrates that the conjugation plays a crucial role in ion-in-materials promoting ternary RRAM devices and highperformance gas sensors manufacture.     

Ternary Flexible Electro‐resistive Memory Device based on Small Molecules

Flexible memory devices have continued to attract more attention due to the increasing requirement for miniaturization, flexibility, and portability for further electronic applications. However, all reported flexible memory devices have binary memory characteristics, which cannot meet the demand of ever‐growing information explosion. Organic resistive switching random access memory (RRAM) has plenty of advantages such as simple structure, facile processing, low power consumption, high packaging density, as well as the ability to store multiple states per bit (multilevel). In this study, we report a small molecule‐based flexible ternary memory device for the first time. The flexible device maintains its ternary memory behavior under different bending conditions and within 500 bending cycles. The length of the alkyl chains in the molecular backbone play a significant role in molecular stacking, thus guaranteeing satisfactory memory and mechanical properties.     

Impact of Top Electrodes (Cu,Ag, and Al) on Resistive Switching behaviour of Cu-rich Cu2ZnSnS4 (CZTS) Ideal Kesterite

Cu₂ZnSnS₄ (CZTS) active material-based resistive random-access memory (RRAM) devices are investigated to understand the impact of three different Cu, Ag, and Al top electrodes. The dual resistance switching (RS) behaviour of spin coated CZTS on ITO/Glass is investigated up to 10² cycles. The stability of all the devices (Cu/CZTS/ITO, Ag/CZTS/ITO, and Al/CZTS/ITO) is investigated up to 10³ sec in low- (LRS) and high- (HRS) resistance states at 0.2 V read voltage. The endurance up to 10² cycles with 30 msec switching width shows stable write and erase current. Weibull cumulative distribution plots suggest that Ag top electrode is relatively more stable for set and reset state with 33.61 and 25.02 shape factors, respectively. The charge carrier transportation is explained by double logarithmic plots, Schottky emission plots, and band diagrams, substantiating that at lower applied electric field intrinsic copper ions dominate in Cu/CZTS/ITO, whereas, at higher electric filed, top electrodes (Cu and Ag) dominate over intrinsic copper ions. Intrinsic Cu⁺ in CZTS plays a decisive role in resistive switching with Al electrode. Further, the impedance spectroscopy measurements suggest that Cu⁺ and Ag⁺ diffusion is the main source for the resistive switching with Cu and Ag electrodes.     

Upgrading Electroresistive Memory from Binary to Ternary Through Single‐Atom Substitution in the Molecular Design

Herein, two molecules based on urea and thiourea, which differ by only a single atom, were designed, successfully synthesized, and fabricated into resistive random‐access memory devices (RRAM). The urea‐based molecule showed binary write‐once‐read‐many (WORM) storage behavior, whereas the thiourea‐based molecule demonstrated ternary storage behavior. Atomic‐force microscopy (AFM) and X‐ray diffraction (XRD) patterns show that both molecules have smooth morphology and ordered layer‐by‐layer lamellar packing, which is beneficial for charge transportation and, consequently, device performance. Additionally, the optical and electrochemical properties indicate that the thiourea‐based molecule has a lower bandgap and may be polarized by trapped charges, thus the formation of a continuous conductive channel and electric switching occurs at lower bias voltage, which results in ternary WORM behavior. This study, together with our previous work on single‐atom substitution, may be useful to tune and improve device performance in the future design of organic memory.     

MoTe2-based low energy consumption artificial synapse for neuromorphic behavior and decimal arithmetic

Two-dimensional material-based memristors have shown attractive research prospects as brain-like devices for neuromorphic computing. Among them, transition metal dichalcogenides–based memristors have proved to be one of the most promising competitors. In this work, a two-dimensional memristor based on MoTe₂ nanosheets was fabricated and demonstrated. The experimental results illustrate that the two-terminal synaptic based on the Ag/MoTe₂/ITO structure exhibits stable bipolar and non-volatile resistive switching characteristics attributed to the controllable formation and rupturing of silver conductive filaments. The device can be successively modulated by a pulse train with a minimum pulse width of 40 ns. More interestingly, the energy consumption of the device to complete one write event is only 74.2 pJ. In addition, biological synaptic behaviors, such as excitatory postsynaptic current gain properties, long-term potentiation (LTP)/long-term depression, spike-timing-dependent- plasticity, short-term plasticity, long-term potentiation (LTP), paired-pulse facilitation, post-tetanic potentiation, and learning-experimental behaviors were mimicked faithfully. Finally, the decimal arithmetic application was introduced to the device, and it is confirmed that addition and multiplication functions can be performed. Therefore, the artificial synapse based on MoTe₂ nanosheets not only exhibits the stable non-volatile resistive switching behavior but also facilitates the development of low-energy consumption neuromorphic computing chips based on transition metal dichalcogenides.