Oligosaccharide Carbohydrate Dielectrics toward High-Performance Non-volatile Transistor Memory Devices

A Green High-k Dielectric from Modified Carboxymethyl Cellulose-Based with Dextrin

Many crucial components inside electronic devices are made from non-renewable, non-biodegradable, and potentially toxic materials, leading to environmental damage. Finding alternative green dielectric materials is mandatory to align with global sustainable goals. Carboxymethyl cellulose (CMC) is a bio-polymer derived from cellulose and has outstanding properties. Herein, citric acid, dextrin, and CMC based hydrogels are prepared, which are biocompatible and biodegradable and exhibit rubber-like mechanical properties, with Young modulus values of 0.89 MPa. Hence, thin film CMC-based hydrogel is explored as a suitable green high-k dielectric candidate for operation at low voltages, demonstrating a high dielectric constant of up to 78. These fabricated transistors reveal stable high capacitance (2090 nF cm-2) for ≈±3 V operation. Using a polyelectrolyte-type approach and poly-(2-vinyl anthracene) (PVAn) surface modification, this study demonstrates a thin dielectric layer (d ≈30 nm) with a small voltage threshold (Vth ≈-0.8 V), moderate transconductance (gm ≈65 nS), and high ON-OFF ratio (≈105). Furthermore, the dielectric layer exhibits stable performance under bias stress of ± 3.5 V and 100 cycles of switching tests. The modified CMC-based hydrogel demonstrates desirable performance as a green dielectric for low-voltage operation, further highlighting its biocompatibility.

A floating-gate field-effect transistor memory device based on organic crystals with a built-in tunneling dielectric by a one-step growth strategy

A floating-gate organic field-effect transistor (FG-OFET) memory device is becoming a promising candidate for emerging non-volatile memory applications due to the advantages of its sophisticated data-storage mechanism and reliable long-term data retention capacity. However, a conventional FG-OFET memory device suffers from complex fabrication technologies and poor mechanical flexibility, which limits its practical applications. Here, we propose a facile one-step liquid-surface drag coating strategy to fabricate a layered stack of 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (Dif-TES-ADT) crystals and high-quality insulating polymer polystyrene (PS). The liquid surface enhances the spreading area of an organic solution and facilitates the unidirectional growth of organic crystals. In the bilayer-structured blend, the bottom PS polymer and the top Dif-TES-ADT semiconductor serve as a tunneling dielectric and an active memory layer of an FG-OFET memory device, respectively. Consequently, a flexible FG-OFET memory device with a large memory window of 41.4 V, a long retention time of 5000 s, and a high current ON/OFF ratio of 105 could be achieved, showing the best performance ever reported for organic thin film-based FG-OFET memory devices. In addition, multi-level data storage (3 bits per cell) can be achieved by tuning the gate voltage magnitude. Our work not only provides a general strategy for the growth of high-quality organic crystals, but also paves the way towards high-performance flexible memory devices.

Advances in Emerging Photonic Memristive and Memristive-Like Devices

Possessing the merits of high efficiency, low consumption, and versatility, emerging photonic memristive and memristive-like devices exhibit an attractive future in constructing novel neuromorphic computing and miniaturized bionic electronic system. Recently, the potential of various emerging materials and structures for photonic memristive and memristive-like devices has attracted tremendous research efforts, generating various novel theories, mechanisms, and applications. Limited by the ambiguity of the mechanism and the reliability of the material, the development and commercialization of such devices are still rare and in their infancy. Therefore, a detailed and systematic review of photonic memristive and memristive-like devices is needed to further promote its development. In this review, the resistive switching mechanisms of photonic memristive and memristive-like devices are first elaborated. Then, a systematic investigation of the active materials, which induce a pivotal influence in the overall performance of photonic memristive and memristive-like devices, is highlighted and evaluated in various indicators. Finally, the recent advanced applications are summarized and discussed. In a word, it is believed that this review provides an extensive impact on many fields of photonic memristive and memristive-like devices, and lay a foundation for academic research and commercial applications.

Tailored Solid-State Carbohydrate Nanostructures Based on Star-Shaped Discrete Block Co-Oligomers

Carbohydrates are key building blocks for advanced functional materials owing to their biological functions and unique material properties. Here, we propose a star-shaped discrete block co-oligomer (BCO) platform to access carbohydrate nanostructures in bulk and thin-film states via the microphase separation of immiscible carbohydrate and hydrophobic blocks (maltooligosaccharides with 1-4 glucose units and solanesol, respectively). BCOs with various star-shaped architectures and saccharide volume fractions were synthesized using a modular approach. In the bulk, the BCOs self-assembled into common lamellar, cylindrical, and spherical carbohydrate microdomains as well as double gyroid, hexagonally perforated lamellar, and Fddd network morphologies with domain spacings of ∼7 nm. In thin films, long-range-ordered periodic carbohydrate microdomains were fabricated via spin coating. Such controlled spatial arrangements of functional carbohydrate moieties on the nanoscale have great application potential in biomedical and nanofabrication fields.

Harnessing of Spatially Confined Perovskite Nanocrystals Using Polysaccharide-based Block Copolymer Systems

Metal halide perovskite nanocrystals (PVSK NCs) are generally unstable upon their transfer from colloidal dispersions to thin film devices. This has been a major obstacle limiting their widespread application. In this study, we proposed a new approach to maintain their exceptional optoelectronic properties during this transfer by dispersing brightly emitting cesium lead halide PVSK NCs in polysaccharide-based maltoheptaose-block-polyisoprene-block-maltoheptaose (MH-b-PI-b-MH) triblock copolymer (BCP) matrices. Instantaneous crystallization of ion precursors with favorable coordination to the sugar (maltoheptaose) domains produced ordered NCs with varied nanostructures of controlled domain size (≈10-20 nm). Confining highly ordered and low dimension PVSK NCs in polysaccharide-based BCPs constituted a powerful tool to control the self-assembly of BCPs and PVSK NCs into predictable structures. Consequently, the hybrid thin films exhibited excellent durability to humidity and stretchability with a relatively high PL intensity and photoluminescence quantum yield (>70%). Furthermore, stretchable phototransistor memory devices were produced and maintained with a good memory ratio of 10⁵ and exhibited a long-term memory retention over 10⁴ s at a high strain of 100%.

Vertically stacked, low-voltage organic ternary logic circuits including nonvolatile floating-gate memory transistors

Multi-valued logic (MVL) circuits based on heterojunction transistor (HTR) have emerged as an effective strategy for high-density information processing without increasing the circuit complexity. Herein, an organic ternary logic inverter (T-inverter) is demonstrated, where a nonvolatile floating-gate flash memory is employed to control the channel conductance systematically, thus realizing the stabilized T-inverter operation. The 3-dimensional (3D) T-inverter is fabricated in a vertically stacked form based on all-dry processes, which enables the high-density integration with high device uniformity. In the flash memory, ultrathin polymer dielectrics are utilized to reduce the programming/erasing voltage as well as operating voltage. With the optimum programming state, the 3D T-inverter fulfills all the important requirements such as full-swing operation, optimum intermediate logic value (~V_DD/2), high DC gain exceeding 20 V/V as well as low-voltage operation (< 5 V). The organic flash memory exhibits long retention characteristics (current change less than 10% after 10⁴s), leading to the long-term stability of the 3D T-inverter. We believe the 3D T-inverter employing flash memory developed in this study can provide a useful insight to achieve high-performance MVL circuits.

High-density information processing without increasing the circuit complexity is highly desired in electronics. Here, Im et al. demonstrate a low-voltage organic ternary logic circuit vertically integrated with the nonvolatile flash memory, increasing the information density by a factor of 3.

Panchromatic Fluorescence Emission from Thienosquaraines Dyes: White Light Electrofluorochromic Devices

Electrofluorochromic devices (EFCDs) that allow the modulation of the light emitted by electroactive fluorophores are very attractive in the research field of optoelectronics. Here, the electrofluorochromic behaviour of a series of squaraine dyes was studied for the first time. In solutions, all compounds are photoluminescent with maxima located in the range 665-690 nm, characterized by quantum yields ranging from 30% to 4.1%. Squaraines were incorporated in a polymer gel used as an active layer in all-in-one gel switchable EFCDs. An aggregation induced quenching occurs in the gel phase, causing a significant decrease in the emission quantum yield in the device. However, the squaraines containing the thieno groups (thienosquaraines, TSQs) show a panchromatic emission and their electrofluorochromism allows the tuning of the fluorescence intensity from 500 nm to the near infrared. Indeed, the application of a potential difference to the device induces a reversible quenching of their emission that is significantly higher and occurs at shorter switching times for TSQs-based devices compared to the reference squaraine dye (DIBSQ). Interestingly, the TSQs fluorescence spectral profile becomes more structured under voltage, and this could be explained by the shift of the aggregates/monomer equilibrium toward the monomeric species, due to electrochemical oxidation, which causes the disassembling of aggregates. This effect may be used to modulate the colour of the fluorescence light emitted by a device and paves the way for conceiving new electrofluorochromic materials based on this mechanism.

Trap-Assisted Charge Storage in Titania Nanocrystals toward Optoelectronic Nonvolatile Memory

Transistor-based memories are of particular significance in the pursuit of next-generation nonvolatile memories. The charge storage medium in a transistor-based memory is pivotal to the device performance. In this report, nitrogen doping titania nanocrystals (N-TiO₂ NCs) synthesized through a low-temperature nonhydrolytic method are used as the charge storage medium in a graphene transistor-based memory. The decoration of the N-TiO₂ NCs enables the device to perform as an ultraviolet (UV) light-programmable nonvolatile optoelectronic memory. Multilevel nonvolatile information recording can be realized through accurate control of the incident light dose, which is ascribed to the vast and firm hole trapping abilities of the N-TiO₂ NCs induced by the N dopant. Accordingly, a positive gate voltage can be used to erase the programmed state by promoting the recombination of stored holes in N-TiO₂ NCs. This study manifests the importance of trap engineering for information storage and provides an alternative path toward nonvolatile optoelectronic memory.

Recent Advances in Biomolecule-Nanomaterial Heterolayer-Based Charge Storage Devices for Bioelectronic Applications

With the acceleration of the Fourth Industrial Revolution, the development of information and communications technology requires innovative information storage devices and processing devices with low power and ultrahigh stability. Accordingly, bioelectronic devices have gained considerable attention as a promising alternative to silicon-based devices because of their various applications, including human-body-attached devices, biomaterial-based computation systems, and biomaterial-nanomaterial hybrid-based charge storage devices. Nanomaterial-based charge storage devices have witnessed considerable development owing to their similarity to conventional charge storage devices and their ease of applicability. The introduction of a biomaterial-to-nanomaterial-based system using a combination of biomolecules and nanostructures provides outstanding electrochemical, electrical, and optical properties that can be applied to the fabrication of charge storage devices. Here, we describe the recent advances in charge storage devices containing a biomolecule and nanoparticle heterolayer including (1) electrical resistive charge storage devices, (2) electrochemical biomemory devices, (3) field-effect transistors, and (4) biomemristors. Progress in biomolecule-nanomaterial heterolayer-based charge storage devices will lead to unprecedented opportunities for the integration of information and communications technology, biotechnology, and nanotechnology for the Fourth Industrial Revolution.

Solution-Processable Anion-doped Conjugated Polymer for Nonvolatile Organic Transistor Memory with Synaptic Behaviors

Brain-inspired synaptic transistors have been considered as a promising device for next-generation electronics. To mimic the behavior of a biological synapse, both data processing and nonvolatile memory capability are simultaneously required for a single electronic device. In this work, a simple approach to realize a synaptic transistor with improved memory characteristics is demonstrated by doping an ionic additive, tetrabutylammonium perchlorate (TBAP), into an active polymer semiconductor without using any extra charge storage layer. TBAP doping is first revealed to improve the memory window of a derived transistor memory device from 19 to 32 V (∼68% enhancement) with an on/off current ratio over 10³ at V_G = -10 V. Through morphological analysis and theoretical calculations, it is revealed that the association of anion with polymers enhances the charge retention capability of the polymer and facilitates the interchain interactions to result in improved memory characteristics. More critically, the doped device is shown to successfully mimic the synaptic behaviors, such as paired-pulse facilitation (PPF), excitatory and inhibitory postsynaptic currents, and spike-rate dependent plasticity. Notably, the TBAP-doped device is shown to deliver a PPF index of up to 204% in contrast to the negligible value of an undoped device. This study describes a novel approach to prepare a synaptic transistor by doping conjugated polymers, which can promote the future development of artificial neuromorphic systems.

Nanostructure- and Orientation-Controlled Resistive Memory Behaviors of Carbohydrate-block-Polystyrene with Different Molecular Weights via Solvent Annealing

We report the resistive electrical memory characteristics controlled by the self-assembled nanostructures of maltoheptaose-block-polystyrene (MH-b-PS) block copolymers, where the MH and PS blocks provide the charge-trapping and the insulating tunneling layer, respectively. A simple solvent annealing process, with various annealing conditions, were introduced for MH-b-PS thin films to achieve disordered, orientated cylinders and ordered-packed spheres morphologies. More details about the self-assembled MH-b-PS nanostructures, coupled with different volume fractions between MH and PS blocks, were investigated using atomic force microscopy and grazing-incidence small-angle X-ray scattering analyses. Moreover, various electrical memory behaviors including nonvolatile write-once-read-many-times (WORM) and Flash, and volatile dynamic-random-access-memory (DRAM) could be obtained by the same material (MH-b-PS_3k). This study establishes a detailed relationship between the nanostructure of the MH-b-PS-based block copolymers and their memory behavior of the resistive memory devices.

Interface Engineering in Organic Field-Effect Transistors: Principles, Applications, and Perspectives

Heterogeneous interfaces that are ubiquitous in optoelectronic devices play a key role in the device performance and have led to the prosperity of today's microelectronics. Interface engineering provides an effective and promising approach to enhancing the device performance of organic field-effect transistors (OFETs) and even developing new functions. In fact, researchers from different disciplines have devoted considerable attention to this concept, which has started to evolve from simple improvement of the device performance to sophisticated construction of novel functionalities, indicating great potential for further applications in broad areas ranging from integrated circuits and energy conversion to catalysis and chemical/biological sensors. In this review article, we provide a timely and comprehensive overview of current efficient approaches developed for building various delicate functional interfaces in OFETs, including interfaces within the semiconductor layers, semiconductor/electrode interfaces, semiconductor/dielectric interfaces, and semiconductor/environment interfaces. We also highlight the major contributions and new concepts of integrating molecular functionalities into electrical circuits, which have been neglected in most previous reviews. This review will provide a fundamental understanding of the interplay between the molecular structure, assembly, and emergent functions at the molecular level and consequently offer novel insights into designing a new generation of multifunctional integrated circuits and sensors toward practical applications.

Building memory devices from biocomposite electronic materials

Natural biomaterials are potential candidates for the next generation of green electronics due to their biocompatibility and biodegradability. On the other hand, the application of biocomposite systems in information storage, photoelectrochemical sensing, and biomedicine has further promoted the progress of environmentally benign bioelectronics. Here, we mainly review recent progress in the development of biocomposites in data storage, focusing on the application of biocomposites in resistive random-access memory (RRAM) and field effect transistors (FET) with their device structure, working mechanism, flexibility, transient characteristics. Specifically, we discuss the application of biocomposite-based non-volatile memories for simulating biological synapse. Finally, the application prospect and development potential of biocomposites are presented.

Logic Gate Functions Built with Nonvolatile Resistive Switching and Thermoresponsive Memory Based on Biologic Proteins

Logic gate functions built with nonvolatile resistive switching and thermoresponsive memory based on biologic proteins were investigated. The "NAND" and "NOR" functions of logic gates in soya protein devices have been built at room temperature by their nonvolatile ternary WORM resistive switching behaviors. Furthermore, heating the devices from room temperature to 358 K results in a switch from tristable state to bistable state WORM resistive switching behavior, indicating that the thermoresponsiveness can be efficiently memorized. The biologic transient nonvolatile memory device consisting of soya protein is illustrated. This device exhibits a long data retention time (104 s) and significant HRS/LRS ratio (∼105); the transient response of the current to voltage of an as-fabricated device is also explored. The soya protein based memory device on a gelatin film substrate is also assessed to validate the feasibility of degradation and biological compatibility for the implantable biological electronic device, that is, innoxious and avirulent to the human body. This can offer alternative avenues for exploring prospective bioelectronic devices.

Electroluminochromic Materials and Devices Based on Metal Complexes

Electroluminochromism (ELC) refers to an interesting phenomenon exhibited by a material whose luminescent properties can be reversibly modulated under an electrical stimulus. Such a luminescence-switching property has been widely used in various organic optoelectronic devices because it can simultaneously detect electrical and optical signals. Metal complexes are the promising candidates for ELC materials due to their sensitivity to an electrical stimulus. Herein, recent progress on electroluminochromic materials and devices based on various metal complexes has been summarized. Meanwhile, the applications of these complexes in data recording and security protection have also been discussed. Finally, a brief conclusion and outlook are presented, pointing out that the development of electroluminochromic metal complexes with excellent performance is important because they play a vital role in future intelligent optoelectronic devices.

Low temperature below 200 °C solution processed tunable flash memory device without tunneling and blocking layer

Intrinsic charge trap capacitive non-volatile flash memories take a significant share of the semiconductor electronics market today. It is challenging to create intrinsic traps in the dielectric layer without high temperature processing steps. The main issue is to optimize the leakage current and intrinsic trap density simultaneously. Moreover, conventional memory devices need the support of tunneling and blocking layers since the charge trapping dielectric layer is incapable of preventing the memory leakage. Here we report a tunable flash memory device without tunneling and blocking layer by combining the discovery of high intrinsic charge traps of more than 10¹² cm^-2, together with low leakage current of less than 10^-7 A cm^-2 in solution derived, inorganic, spin-coated dielectric films which were heated at 200 °C or below. In addition, the memory storage capacity is tuned systematically upto 96% by controlling the trap density with increasing heating temperature.

Phototunable Biomemory Based on Light-Mediated Charge Trap

Phototunable biomaterial-based resistive memory devices and understanding of their underlying switching mechanisms may pave a way toward new paradigm of smart and green electronics. Here, resistive switching behavior of photonic biomemory based on a novel structure of metal anode/carbon dots (CDs)-silk protein/indium tin oxide is systematically investigated, with Al, Au, and Ag anodes as case studies. The charge trapping/detrapping and metal filaments formation/rupture are observed by in situ Kelvin probe force microscopy investigations and scanning electron microscopy and energy-dispersive spectroscopy microanalysis, which demonstrates that the resistive switching behavior of Al, Au anode-based device are related to the space-charge-limited-conduction, while electrochemical metallization is the main mechanism for resistive transitions of Ag anode-based devices. Incorporation of CDs with light-adjustable charge trapping capacity is found to be responsible for phototunable resistive switching properties of CDs-based resistive random access memory by performing the ultraviolet light illumination studies on as-fabricated devices. The synergistic effect of photovoltaics and photogating can effectively enhance the internal electrical field to reduce the switching voltage. This demonstration provides a practical route for next-generation biocompatible electronics.

Utilization of Electrochromically Luminescent Transition-Metal Complexes for Erasable Information Recording and Temperature-Related Information Protection

Transition metal complexes containing pyrazinium or pyridinium moieties display reversible luminescence changes in response to electrical stimuli, which is useful in the development of erasable information recording electric devices. These complexes are also suitable for temperature-related information protection, since chemically-induced luminescence turn-on is temperature-dependent.

Non-volatile transistor memory devices using charge storage cross-linked core-shell nanoparticles

Solution processable cross-linked core-shell poly[poly(ethylene glycol)methylether methacrylate]-block-poly(2,5-dibromo-3-vinylthiophene) (poly(PEGMA)m-b-poly(DB3VT)n) nanoparticles are firstly explored as charge storage materials for transistor-type memory devices owing to their efficient and controllable ability in electric charge transfer and trapping.