Organic Memory Research Articles

기록기술의 발전과 기억: 라이프로그와 디지털적 기억의 양면성

This paper examines the problems of the lifelog, the digital recording of everyday life, now increasingly used by the younger generation, and digital memory, based on Ted Chang's novel The Truth of Fact, The Truth of Feeling. In the futuristic novel in which human memory work based on association and reconstruction has been supplemented and replaced by the new software search tool, Remem, the author deals with the reality that human organic memory is gradually replaced by digital memory: In the alternative reality one thinks organic memory is fallible, whereas the digital memory is completely accurate. This paper first examines the correlation between the development of writing technology and change in the form of memory, and secondly critically analyzes where the accuracy of digital memory comes from, and finally elucidates that fallible and emotional biological memory plays a decisive role in human autobiographical narrative and identity formation.

Molecular-Shape-Controlled Binary to Ternary Resistive Random-Access Memory Switching of N-Containing Heteroaromatic Semiconductors.

In organic resistive random-access memory (ReRAM) devices, deeply understanding how to control the performance of π-conjugated semiconductors through molecular-shape-engineering is important and highly desirable. Herein, we design a family of N-containing heteroaromatic semiconductors with molecular shapes moving from mono-branched 1Q to di-branched 2Q and tri-branched 3Q. We find that this molecular-shape engineering can induce reliable binary to ternary ReRAM switching, affording a highly enhanced device yield that satisfies the practical requirement. The density functional theory calculation and experimental evidence suggest that the increased multiple paired electroactive nitrogen sites from mono-branched 1Q to tri-branched 3Q are responsible for the multilevel resistance switching, offering stable bidentate coordination with the active metal atoms. This study sheds light on the prospect of N-containing heteroaromatic semiconductors for promising ultrahigh-density data-storage ReRAM application.

Condensation Recondensed

Adaptations are, in a sense, multi-layered vehicles for memories of literary (or other) originals. The audience’s memories of different media versions of the classic text coexist, compete and converge, creating an extensive multi-dimensional experience. How does their memory work when readers become viewers (or vice versa) and recondense many ideas, images, and feelings linked to specific narrative worlds? The paper centres around two metaphors for memory regimes – present explicitly or implicitly – in contemporary adaptation studies. The regime of a palimpsest is based on the organic memory; it describes the individual perception of narratives: the memory of the viewer or the reader activates the intertextual “richness” of the adaptation, comparing/juxtaposing/merging different media versions of one narrative world. The regime of a network regulates the “life” of narratives in collective/cultural memory, the way meaning is ascribed to particular stories throughout the centuries, and the mechanisms of production and dissemination of narratives by the cultural industries. Metaphors help elaborate on the differentiation between the individual and the collective, the fixed and the fluid in the process of adapting, between the conventional and the contingent. Through the analyses of four film adaptations of Romeo and Juliet and a recent TV series, using the tragedy’s motifs, this paper shows how the network regime uncovers ways to make the viewer’s memory “get side-tracked”, and recall what the viewer is unlikely to remember. Via networks adaptations make their audiences remember “prosthetically” and learn more about “real” spaces with their real problems, while being initially trapped into viewing by the familiarity of old fictional stories.

Low-voltage, solution-processed, two-terminal organic bistable memory device

An low-voltage, solution-based spin cast-processed two-terminal bi-stable memory device was fabricated by using organic-inorganic-organic tri-layer structure (MEHPPV/ZnO/MEHPPV) onto indium tin oxide coated glass. Tri-layer device structure displayed the significant switching characteristics. The absence of degradation after 1 h retention test at 120 °C was noticed. The consistent memory behavior was noticed even after 50 cycles. Electron tunneling mechanism was utilized for describing switching mechanism of the device. The result emphasizes that the class of memory devices have been fabricated with organic-inorganic-organic nanocomposites, which has led to considerable research and development efforts to the scene of latent applications.

Robust Radical Cations of Hexabenzoperylene Exhibiting High Conductivity and Enabling an Organic Nonvolatile Optoelectronic Memory.

Herein, we report robust π-conjugated radical cations resulting from the oxidation of hexabenzoperylene (HBP) derivatives, HBP-B and HBP-H, which have butyl and hexyl groups, respectively, attached to the same twisted double helicene π-backbone. The radical cation of HBP-B was successfully crystallized in the form of hexafluorophosphate, which exhibited conductivity as high as 1.32 ± 0.04 S cm-1. Photochemical oxidation of HBP-H by molecular oxygen led to the formation of its radical cation in the solid state, as found with different techniques. This allowed the organic field effect transistor of HBP-H to function as a nonvolatile optoelectronic memory, with the memory switching contrast above 103 and long-term stability without using a floating gate, an electret layer, or photochromic molecules.

An organic ambipolar charge trapping non-volatile memory device based on double heterojunctions

An organic ambipolar charge trapping non-volatile memory device is proposed based on tris(8-hydroxy quinoline) aluminum(Alq3)/ fullerene(C60)/pentacene double heterojunctions. The double heterojunctions were analyzed and compared with the sole heterojunction. Even though the Alq3/pentacene sole heterojunction shows a negative threshold voltage shift for programming under negative biasing, light illumination is required to efficiently erase. In contrast, for C60/pentacene sole heterojunction, the negative shift of threshold voltage is observed even with a positive erasing voltage. By combining the two trapping layers, a large memory window with fully-electrical programming and erasing is obtained. The efficient programming and erasing of the double heterojunctions structure are analyzed, sufficient electrons can be injected that enables the electrical erasing, and the negative shift of the threshold voltage under positive erasing voltage for the C60/pentacene structure is suppressed due to the suppression of the large built-in potential for the sole heterojunction, which can be verified by a large positive shift for the pentacene/C60/pentacene double heterojunctions.

High-speed, low-voltage programmable/erasable flexible 2-bit organic transistor nonvolatile memory with a monolayer buffered ferroelectric terpolymer insulator

Achieving multi-bit data storage in one transistor is a promising strategy to further multiply the storage density of the nonvolatile memories (NVMs). Low-voltage programming/erasing (P/E) operation is a prerequisite for the commercialization of the multi-bit NVMs. And, the fast P/E switching is also a desirable figure of merit for the practical NVMs. Here, we develop a route to achieve a high-speed, low-voltage P/E flexible organic transistor-based NVM, by processing a monolayer buffered ferroelectric terpolymer insulator. The physical mechanisms for achieving the high-speed, low-voltage P/E properties in the organic transistor-based NVMs are investigated. As a result, high-performance flexible 2-bit NVMs are achieved, with the low P/E voltage of ±15 V, fast P/E switching capability of 50 ns, high mobility up to 7.4 cm2 V−1 s−1, high stable retention time up to 10 years, reliable endurance over 200 cycles, good mechanical bending durability, and atmosphere stability.

Development of Multilevel Organic Phototransistor Memory using Conjugated/Insulating Polymer Blends with a Vertical Phase Separation

AbstractIn this work, a series of methacrylate‐based polymers bearing benzene (poly(benzyl methacrylate)), naphthalene (poly(2‐naphthyl methacrylate)), anthracene (poly(9‐anthracenyl methyl methacrylate), PAMA), and pyrene (poly(1‐pyrenemethyl methacrylate)) are blended with conjugated polymer of poly(3‐hexylthiophene) (P3HT) to perform vertical phase separation during spin‐coating. The bilayer structure of the conjugated/insulating polymer blend is driven by their mismatch in surface energy, and the blend films are applied in the phototransistor memory device with the bottom layer of methacrylate‐based polymer as a photoactive electret and the top layer of P3HT as a semiconducting channel. It is found that the vertical phase separation morphology, conjugation, and energy levels of the pendant arene groups in the methacrylate‐based polymers are highly related to the photoresponse, memory retention/endurance of the phototransistor memory. Therefore, the device comprising the polymer blend of P3HT and PAMA successfully produces a high current contrast of 105 to 254 nm light and 104 to 450 nm light over 104 s. This study provides a facile approach to the fabrication of high‐performance phototransistor memory devices.

Enhancement of resistive switching behavior of organic resistive random access memory devices through UV-Ozone treatment

We fabricated organic resistive random-access memory (RRAM) devices using a low-cost solution-process method. All the processes were performed at temperatures below 135 °C under ambient atmospheric conditions. The RRAM resistive switching layer was formed from a polymer-fullerene bulk heterojunction using poly(3-hexylthiophene-2,5-diyl) (P3HT) and (6,6)-phenyl C61 butyric acid methyl ester (PCBM). The fabricated organic RRAM device exhibited typical nonvolatile bipolar resistive switching behavior with an ON/OFF ratio of ∼40, but it provided a low endurance of 27 cycles. Therefore, for enhanced stability, simple UV–Ozone (UVO) treatment was applied to the P3HT:PCBM organic bulk heterojunction layer. The organic RRAM device with UVO treatment exhibited an enhanced performance with an ON/OFF ratio of ∼400 and an endurance of 47 cycles. In addition, complementary resistive switching behavior was observed. The conduction mechanisms of the organic RRAM device were investigated by fitting the measured I–V data to numerical equations, and Schottky emission and Ohmic conduction were the main conduction mechanisms for the high-resistance and low-resistance states for the RRAM device with or without UVO treatment.

Unraveling the Role of Polydopamines in Resistive Switching in Al/Polydopamine/Al Structure for Organic Resistive Random-Access Memory.

In an era of rapidly evolving artificial intelligence and 5G communications technologies, massive data storage and processing are required for the real-time operation of digital processors in conventional wearable devices. However, classical von-Neumann architecture computers are limited by bottleneck-related issues. As a solution, resistive random-access memory (RRAM) devices are being considered as next generation in-memory computing devices. Among various materials, a polydopamine (PDA) is an attractive candidate for the fabrication of wearable and flexible RRAM devices. Herein, an aluminum/PDA/aluminum structure is proposed to investigate the influence of the PDA layer on resistive switching. The resistance-switching characteristics of an Al/PDA/Al structure are investigated by changing the PDA’s coating time and an on/off ratio of 2.48 × 103 is recorded. X-ray photoelectron spectroscopy reveals the presence of an Al2O3 layer in Al/PDA/Al structure, and the contents of oxygen vacancies are changed according to PDA coating time. Conductive filaments in the PDA/Al structure are confirmed by conductive atomic-force microscopy. As an application, a flexible Al/PDA/Al structure is fabricated using polyethylene terephthalate substrate and its operation is successfully confirmed. These results describe the resistive-switching characteristics, including oxygen vacancies, of Al/PDA/Al structures and provide new ways of understanding the resistive-switching mechanism of PDA-based RRAM devices.

High On/Off Ratio Organic Resistive Switching Memory Based on Carbazolyl Dicyanobenzene and a Polymer Composite

High On/Off Ratio Organic Resistive Switching Memory Based on Carbazolyl Dicyanobenzene and a Polymer Composite

Enhanced intra/intermolecular charge transfer for efficient multilevel resistive memory

Adjustment of molecular structure can effectively improve the organic memory device behaviors due to the optimization of intra/intermolecular interaction and molecular packing motif. However, the intrinsic mechanism of how intermolecular interaction and molecular packing motif affect the device performance needs to be further explored. Herein, we synthesized four new small molecules (X-TEBT) by introducing the alkynyl π bridges and different substituents (X = H, CN, tBu, OMe) into the backbone of conjugated donor–acceptor molecules, namely, TEBT, CN-TEBT, tBu-TEBT and OMe-TEBT, for solution-processed organic resistive memory. All memory devices displayed nonvolatile write-once-read-many-times (WORM) behaviors with low threshold voltage (Vth), high production yield, and good thermal stability. The champion device (tBu-TEBT) exhibits ternary WORM property with the highest ON2/ON1/OFF ratio and the lowest Vth1 (1.6 V) and Vth2 (2.4 V). More importantly, the single crystal structure of tBu-TEBT was successfully obtained which helped us analyze the origin of the physical mechanism of resistive switching behavior and establish a common structure–property relationship for high performance organic memory. Its excellent properties enable us to perform logic gates and information display functions which offer possibilities as smart sensor in Internet of Things (IoT) application.

Photocatalysis‐Induced Nanopores toward Highly Reliable Organic Electrochemical Metallization Memory

AbstractOrganic electrochemical metallization (ECM) memory that possesses high reliable switching performance is in great demand for the future smart wearable and flexible electronics. The resistive switching (RS) behavior of organic ECM memory is determined by the micro‐morphology evolution of metal conductive filaments (CFs) during the operating process. However, the morphology controllability of CFs is generally deteriorated by their random distribution and unexpected overgrowth. Herein, a kind of nanoporous PVC/TiO2 nanocomposite is developed using photocatalytic method for improving the RS reliability of organic ECM memory. The introduction of engineered nanopores can effectively simplify the CFs morphology to obtain excellent uniformity, good retention, and low cycling degradation. In addition, taking advantage of the multilevel RS behavior and 200 × 200 memristive array artificial neural network (ANN), alphabetic data storage and image pattern recognition are successfully realized. The proposed approach is expected to provide novel platforms for the advance of highly reliable flexible electronics and ANN for intelligence applications.

Resistive organic memory devices based on nitrogen-doped CNTs/PSS composites

Resistive organic memory devices based on nitrogen-doped CNTs/PSS composites

Transparent Organic Nonvolatile Memory and Volatile Synaptic Transistors Based on Floating Gate Structure

In order to comply with the rapid development of new-generation electronics, developing memories which could meet the demands for specific application such as flexibility, transparency and neuromorphic functions are of great significance. In this work, a transparent organic nonvolatile memory (transparency≥81%) is developed with Ag nanowire as floating gate layer, which exhibits excellent memory characteristics and mechanical flexibility. Moreover, the transition from memory to artificial synapse is achieved by adjusting the concentration of Ag nanowire. This work provides a new solution for transparent flexible memory and shows their potential for next-generation transparent organic electronics.

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 (~VDD/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 104 s), 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.

Advanced Nonvolatile Organic Optical Memory Using Self-Assembled Monolayers of Porphyrin-Fullerene Dyads.

Photo-switchable organic field-effect transistors (OFETs) represent an important platform for designing memory devices for a diverse array of products including security (brand-protection, copy-protection, keyless entry, etc.), credit cards, tickets, and multiple wearable organic electronics applications. Herein, we present a new concept by introducing self-assembled monolayers of donor–acceptor porphyrin–fullerene dyads as light-responsive triggers modulating the electrical characteristics of OFETs and thus pave the way to the development of advanced nonvolatile optical memory. The devices demonstrated wide memory windows, high programming speeds, and long retention times. Furthermore, we show a remarkable effect of the orientation of the fullerene–polymer dyads at the dielectric/semiconductor interface on the device behavior. In particular, the dyads anchored to the dielectric by the porphyrin part induced a reversible photoelectrical switching of OFETs, which is characteristic of flash memory elements. On the contrary, the devices utilizing the dyad anchored by the fullerene moiety demonstrated irreversible switching, thus operating as read-only memory (ROM). A mechanism explaining this behavior is proposed using theoretical DFT calculations. The results suggest the possibility of revisiting hundreds of known donor–acceptor dyads designed previously for artificial photosynthesis or other purposes as versatile optical triggers in advanced OFET-based multibit memory devices for emerging electronic applications.

Polyelectrolyte Bilayer-Based Transparent and Flexible Memristor for Emulating Synapses.

Memristors will be critical components in the next generation of digital technology and artificial synapses. Researchers are investigating innovative mechanistic understanding of the memristor devices based on low-cost, solution-processable, and organic materials as promising candidates. Here, we demonstrate a novel polyelectrolyte-based memristor device, which is simply prepared by spin-coating poly(acrylic acid) (PAA) and polyethylenimine (PEI) on an indium tin oxide (ITO) substrate followed by a magnetron sputtering of the ITO as the top electrode. The device has a potential to achieve excellent resistive switching (RS) performance and synapse functionality as well as greater flexibility and transmittance when compared to the oxide-based memories. An on/off resistance ratio of 50 can be maintained without degradation for up to 20 000 cycles (flat state) and over 4000 cycles (bending to a 2 mm radius 10 000 times) in the DC sweep mode. Moreover, the device performs various synaptic functions, including spike-timing-dependent plasticity, pulse pair plasticity, and short-term and long-term plasticity in the potentiation and depression processes. The counterions and two oppositely charged polyelectrolyte chains can move in and out of each other depending on the applied electrical potential (pulse), resulting in a change in the potential drop at the interface of the polyelectrolyte bilayer and its electrodes, which can be attributed to the RS mechanism and various synaptic functions. This insight may accelerate the technological deployment of the organic resistive memories.

Water-Soluble Reactive Polymer Blends for Stable Memory Layers in Low-Voltage Nonvolatile Organic Memory Transistors with High Mobility and Data-Retention Characteristics.

Here low-voltage nonvolatile organic memory transistors, featuring high charge-carrier mobility and outstanding data-retention characteristics, by employing water-soluble reactive polymer blends as a gate-insulating memory layer are demonstrated. Blend films of poly(vinyl alcohol) (PVA) and poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPSA) (PVA:PAMPSA) are prepared from their aqueous solutions with various molar ratios of PAMPSA (0-18mol%) and thermally annealed at 70 and 110°C. Organic field-effect transistors (OFETs) are fabricated by depositing poly(3-hexylthiophene) (P3HT) channel layers on the thermally treated PVA:PAMPSA films. Results show that the hole mobility of OFETs is remarkably increased (≈294 times at 70°C and ≈42 times at 110°C) by adding only 2mol% PAMPSA to the PVA films and further improved at 10mol% PAMPSA (>11.7cm2 V-1 s-1 at 70°C and >3.8cm2 V-1 s-1 at 110°C). The hysteresis characteristics are rather strengthened for the PVA:PAMPSA layers by annealing at 110°C due to the formation of cross-linking sites, even though the OFETs with the pristine PVA layers do almost lose hysteresis characteristics at 110°C. The optimized OFETs with the PVA:PAMPSA layers (10mol%, 110°C) deliver excellent data retention characteristics during >10000 memory cycles at a voltage range of -5 to +5V.

Static Response of Three-Dimensional and Printed Complementary Organic TFTs-Based Static Random-Access Memory

A three-dimensional (3-D) and printed static random-access memory (SRAM) based on complementary organic thin-film transistors is demonstrated. The SRAM exhibited the smallest area of 2.1 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , the highest normalized static noise margin of 62%, and the maximum gain of 16.8 V/V compared to the reported values of organic SRAM cells. The transistors’ 3-D integration minimizes the cell area. The 3-D SRAM cell design enables us to match the strengths of transistors by modifying the dielectric thickness without changing the channel geometry. This high-performance complementary organic thin-film transistors-based SRAM shows its high application potential in large-scale and low-cost wearable intelligent electronics for data storage and processing.