Tunable electrical memory characteristics using polyimide:polycyclic aromatic compound blends on flexible substrates

An ultrasmall organic synapse for neuromorphic computing

High-performance organic neuromorphic devices with miniaturized device size and computing capability are essential elements for developing brain-inspired humanoid intelligence technique. However, due to the structural inhomogeneity of most organic materials, downscaling of such devices to nanoscale and their high-density integration into compact matrices with reliable device performance remain challenging at the moment. Herein, based on the design of a semicrystalline polymer PBFCL10 with ordered structure to regulate dense and uniform formation of conductive nanofilaments, we realize an organic synapse with the smallest device dimension of 50 nm and highest integration size of 1 Kb reported thus far. The as-fabricated PBFCL10 synapses can switch between 32 conductance states linearly with a high cycle-to-cycle uniformity of 98.89% and device-to-device uniformity of 99.71%, which are the best results of organic devices. A mixed-signal neuromorphic hardware system based on the organic neuromatrix and FPGA controller is implemented to execute spiking-plasticity-related algorithm for decision-making tasks.

Embedding Azobenzol-Decorated Tetraphenylethylene into the Polymer Matrix to Implement a Ternary Memory Device with High Working Temperature/Humidity

The development of new high-density memories that can work in harsh environments such as high temperature and humidity will be significant for some special occasions such as oil and geothermal industries. Herein, a facial strategy for implementing a ternary memory device with high working temperature/humidity was executed. In detail, an asymmetric aggregation-induced-emission active molecule (azobenzol-decorated tetraphenylethylene, i.e., TPE-Azo) was embedded into flexible poly(ethylene-alt-maleic anhydride) (PEM) to prepare a TPE-Azo@PEM composite, which served as an active layer to fabricate the FTO/TPE-Azo@PEM/Ag device. This device can demonstrate excellent ternary memory performances with a current ratio of 1:10^4.2:10^1.6 for "OFF", "ON1", and "ON2" states. Specially, it can exhibit good environmental endurance at high working temperature (350 °C) and humidity (RH = 90%). The ternary memory mechanism can be explained as the combination of aggregation-induced current/conductance and conformational change-induced charge transfer in the TPE-Azo molecule, which was verified by Kelvin probe force microscopy, UV-vis spectra, X-ray diffraction, and single-crystal structural analysis. This strategy can be used as a universal method for the construction of high-density multilevel memristors with good environmental tolerance.

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.

Organic and hybrid resistive switching materials and devices

This review presents a timely and comprehensive summary of organic and hybrid materials for nonvolatile resistive switching memory applications in the “More than Moore” era, with particular attention on their designing principles for electronic property tuning and flexible memory performance.

Flexible Multifunctional Aromatic Polyimide Film: Highly Efficient Photoluminescence, Resistive Switching Characteristic, and Electroluminescence

We report a flexible multifunctional aromatic polyimide (BTDBPI) that shows yellow-green fluorescence with high photoluminescence quantum yield (PLQY) of 30% in the film state. The nonvolatile "write once-read many" (WORM) characteristic in a memory device with the configuration of ITO/BTDBPI/Au indicates that BTDBPI possesses organic semiconductor behavior. Moreover, polymer light-emitting diodes (PLEDs) with the structure of ITO/PEDOT:PSS/BTDBPI/TPBI/Mg-Ag exhibits an interesting dual-emission phenomenon that originates from the electroluminescence (EL) of the BTDBPI nanometer film (yellow-green, 525 nm) and TPBI (deep blue, 380 nm), demonstrating that BTDBPI shows both the charge-transporting and EL properties.

Changing molecular conjugation with a phenazine acceptor for improvement of small molecule-based organic electronic memory performance

Two small molecules with electron-accepting azobenzene or phenazine blocks, were synthesized. The experimental findings suggest that the molecule with larger conjugation may promote the memory performance by an enhanced strong charge transfer effect.

Nonvolatile ternary resistive switching memory devices based on the polymer composites containing zinc oxide nanoparticles

Nonvolatile ternary memory devices were fabricated from the composites polymer blends containing zinc oxide (ZnO) nanoparticles.

Intrinsically stretchable, solution-processable functional poly(siloxane-imide)s for stretchable resistive memory applications

A stretchable WORM-type resistive memory device was fabricated using poly(siloxane-imide) ODPA-A12 with favorable mechanical properties.

A Low-Temperature, Solution-Processable Organic Electron-Transporting Layer Based on Planar Coronene for High-performance Conventional Perovskite Solar Cells

A low-temperature, solution-processable organic electron-transporting material (ETM) is successfully developed for efficient conventional n-i-p perovskite solar cells (PVSCs). This ETM can show a high efficiency over 17% on rigid device and 14.2% on flexible PVSC. To the best of our knowledge, this efficiency is among the highest values reported for flexible n-i-p PVSCs with negligible hysteresis thus far.

Origin of multi-level switching and telegraphic noise in organic nanocomposite memory devices

The origin of negative differential resistance (NDR) and its derivative intermediate resistive states (IRSs) of nanocomposite memory systems have not been clearly analyzed for the past decade. To address this issue, we investigate the current fluctuations of organic nanocomposite memory devices with NDR and the IRSs under various temperature conditions. The 1/f noise scaling behaviors at various temperature conditions in the IRSs and telegraphic noise in NDR indicate the localized current pathways in the organic nanocomposite layers for each IRS. The clearly observed telegraphic noise with a long characteristic time in NDR at low temperature indicates that the localized current pathways for the IRSs are attributed to trapping/de-trapping at the deep trap levels in NDR. This study will be useful for the development and tuning of multi-bit storable organic nanocomposite memory device systems.

A salification-induced charge transfer effect for improving the resistive memory performance of azo derivative-based devices

We introduce salification to prepare an organic resistive memory material with higher ON/OFF ratio and properties.

Adjusting the Proportion of Electron-Withdrawing Groups in a Graft Functional Polymer for Multilevel Memory Performance

A polymer containing aldehyde active groups (PVB) was synthesized by atom transfer radical polymerization (ATRP), acting as a polymer precursor to graft a functional moiety via nucleophilic addition reaction. DHI (2-(1,5-dimethyl-hexyl)-6-hydrazino-benzo[de]isoquinoline-1,3-dione) and NPH (nitrophenyl hydrazine) groups, which contain naphthalimides that act as narrow traps and nitro groups that act as deep traps, were anchored onto the PVB at different ratios. A series of graft polymers were obtained and named PVB-DHI, PVB-DHI4 -NPH, PVB-DHI-NPH4 , and PVB-NPH. The chemical composition of the polymers was analyzed by (1) H-NMR spectroscopy and X-ray photoelectron spectroscopy (XPS). Memory devices were prepared from the polymers, and I-V characteristics were measured to determine the performance. By adjusting the ratio of different electron acceptors (DHI and NPH) to 4:1, ternary memory behavior was achieved. The relationship between memory behavior of PVB-DHIx NPHy and acceptor groups as well as their conduction mechanism were studied in detail.

Tuning of resistive memory switching in electropolymerized metallopolymeric films

A diruthenium complex capped with two triphenylamine units was polymerized by electrochemical oxidation to afford metallopolymeric films with alternating diruthenium and tetraphenylbenzidine structures. The obtained thin films feature rich redox processes associated with the reduction of the bridging ligands (tetra(pyrid-2-yl)pyrazine) and the oxidation of the tetraphenylbenzidine and diruthenium segments. The sandwiched ITO/polymer film/Al electrical devices show excellent resistive memory switching with a low operational voltage, large ON/OFF current ratio (100-1000), good stability (500 cycles tested), and long retention time. In stark contrast, devices with polymeric films of a related monoruthenium complex show poor memory performance. The mechanism of the field-induced conductivity of the diruthenium polymer film is rationalized by the formation of a charge transfer state, as supported by DFT calculations.

Bistable electrical switching and nonvolatile memory effect in carbon nanotube–poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) composite films

The electrical conductance switching behavior and nonvolatile memory effects in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) PEDOT:PSS and single-wall carbon nanotubes (SWCNTs) composite thin films have been investigated.

Different interactions between a metal electrode and an organic layer and their different electrical bistability performances

Different electrical bistability performances were obtained by tuning metal electrodes.

Resistive switching memory devices based on electrical conductance tuning in poly(4-vinyl phenol)–oxadiazole composites

Nonvolatile memory devices, based on electrical conductance tuning in thin films of poly(4-vinyl phenol) (PVP) and 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) composites, are fabricated.

Adjustment of ON-state retention ability based on new donor-acceptor imides through structural tailoring for volatile device applications

In this study, two D-A molecules NACANA and CANACA, based on carbazole (CA) donor and naphthalimide (NA) acceptor, with different D-A arrangement (A-D-A and D-A-D) were synthesized. The photophysical and electrochemical properties, microstructure and memory behaviors of both A-D-A and D-A-D molecules were systematically investigated. The fabricated devices ITO/NACANA or CANACA layer/Al with a simple sandwich configuration both exhibited volatile nature after shutting off the external electric field. Interestingly, NACANA showed ON-state retention time of ca. 12 min, longer than that of CANACA (ca. 6 min). The difference in retention ability of the programmed states could be assigned to the difference of the D-A arrangement. This type of retention ability adjustment by varying the arrangement of donor and acceptor segments may provide a guide of structure design for future organic-based specific memory devices with tunable volatile property.

Electronic effect of terminal acceptor groups on different organic donor–acceptor small-molecule based memory devices

Three conjugated organic donor–acceptor small-molecules BCZ-BT, BCZ-NO2 and BCZ-CN with different electronic effects in their terminal acceptors were designed and synthesized and their application in memory devices with a sandwich configuration was tested.

Polymer-based resistive memory materials and devices

Due to the advantages of good scalability, flexibility, low cost, ease of processing, 3D-stacking capability, and large capacity for data storage, polymer-based resistive memories have been a promising alternative or supplementary devices to conventional inorganic semiconductor-based memory technology, and attracted significant scientific interest as a new and promising research field. In this review, we first introduced the general characteristics of the device structures and fabrication, memory effects, switching mechanisms, and effects of electrodes on memory properties associated with polymer-based resistive memory devices. Subsequently, the research progress concerning the use of single polymers or polymer composites as active materials for resistive memory devices has been summarized and discussed. In particular, we consider a rational approach to their design and discuss how to realize the excellent memory devices and understand the memory mechanisms. Finally, the current challenges and several possible future research directions in this field have also been discussed.

Nonvolatile organic thin film transistor memory devices based on hybrid nanocomposites of semiconducting polymers: gold nanoparticles

We report the facile fabrication and characteristics of organic thin film transistor (OTFT)-based nonvolatile memory devices using the hybrid nanocomposites of semiconducting poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) and ligand-capped Au nanoparticles (NPs), thereby serving as a charge storage medium. Electrical bias sweep/excitation effectively modulates the current response of hybrid memory devices through the charge transfer between F8T2 channel and functionalized Au NPs trapping sites. The electrical performance of the hybrid memory devices can be effectively controlled though the loading concentrations (0-9 %) of Au NPs and organic thiolate ligands on Au NP surfaces with different carbon chain lengths (Au-L6, Au-L10, and Au-L18). The memory window induced by voltage sweep is considerably increased by the high content of Au NPs or short carbon chain on the ligand. The hybrid nanocomposite of F8T2:9% Au-L6 provides the OTFT memories with a memory window of ~41 V operated at ± 30 V and memory ratio of ~1 × 10(3) maintained for 1 × 10(4) s. The experimental results suggest that the hybrid materials of the functionalized Au NPs in F8T2 matrix have the potential applications for low voltage-driven high performance nonvolatile memory devices.