Flash‐Memory Effect for Polyfluorenes with On‐Chain Iridium(III) Complexes

Polyfluorenes containing Ir(III ) complexes in the main chain are demonstrated to have promising application in a polymer memory device. A flash‐memory device is shown whereby a polymer solution is spin‐coated as the active layer and is sandwiched between an aluminum electrode and an indium tin oxide electrode. This device exhibits very good memory performance, such as low reading, writing, and erasing voltages and a high ON/OFF current ratio of more than 10⁵. Both ON and OFF states are stable under a constant voltage stress of ?1.0 V and survive up to 10⁸ read cycles at a read voltage of ?1.0 V. Charge transfer and traps in polymers are probably responsible for the conductance‐switching behavior and the memory effect. The fluorene moieties act as an electron donor and Ir(III ) complex units as the electron acceptor. Furthermore, through the modification of ligand structures of Ir(III ) complex units, the resulting polymers also exhibit excellent memory behavior. Alteration of ligands can change the threshold voltage of the device. Hence, conjugated polymers containing Ir(III ) complexes, which have been successfully applied in light‐emitting devices, show very promising application in polymer memory devices.     

A Nonvolatile Organic Memory Device Using ITO Surfaces Modified by Ag‐Nanodots

We report on a single‐layer organic memory device made of poly(N‐vinylcarbazole) embedded between an Al electrode and ITO modified with Ag nanodots (Ag‐NDs). Devices exhibit high ON/OFF switching ratios of 10⁴. This level of performance could be achieved by modifying the ITO electrodes with some Ag‐NDs that act as trapping sites, reducing the current in the OFF state. Temperature dependence of the electrical characteristics suggest that the current of the low‐resistance state can be attributed to Schottky charge tunnelling through low‐resistance pathways of Al particles in the polymer layer and that the high‐resistance state can be controlled by charge trapping by the Al particles and Ag‐NDs.     

A flexible polymer memory device

A flexible polymer memory device is demonstrated in a sandwich structure of polypyrrole/P6FBEu/Au. Conductance switching at a voltage of about 4 V, with an ON/OFF current ratio up to 200, was observed in this flexible memory device. At the low-conductivity state, current density–voltage (J–V) characteristics of the device were dominated by a charge injection current. At the high conductivity state, J–V characteristics were dominated by a space-charge-limited current. Both the ON and OFF states are stable up to 10⁶ read cycles at a read voltage of 1 V. The device can be used as a write-once read-many-times (WORM) memory with good electronic stability.     

Conception of Stretchable Resistive Memory Devices Based on Nanostructure‐Controlled Carbohydrate‐block‐Polyisoprene Block Copolymers

It is discovered that the memory‐type behaviors of novel carbohydrate‐block ‐polyisoprene (MH‐b ‐PI) block copolymers‐based devices, including write‐once‐read‐many‐times, Flash, and dynamic‐random‐access‐memory, can be easily controlled by the self‐assembly nanostructures (vertical cylinder, horizontal cylinder, and order‐packed sphere), in which the MH and PI blocks, respectively, provide the charge‐trapping and stretchable function. With increasing the flexible PI block length, the stretchability of the designed copolymers can be significantly improved up to 100% without forming cracks. Thus, intrinsically stretchable resistive memory devices (polydimethylsiloxane(PDMS)/carbon nanotubes(CNTs)/MH‐b ‐PI thin film/Al) using the MH‐b ‐PI thin film as an active layer is successfully fabricated and that using the MH‐b ‐PI_12.6k under 100% strain exhibits an excellent ON/OFF current ratio of over 10⁶ (reading at ?1 V) with stable V _set around ?2 V. Furthermore, the endurance characteristics can be maintained over 500 cycles upon 40% strain. This work establishes and represents a novel avenue for the design of green carbohydrate‐derived and stretchable memory materials.     

Novel Digital Nonvolatile Memory Devices Based on Semiconducting Polymer Thin Films

Recent increases in the demand for mobile devices have stimulated the development of nonvolatile memory devices with high performance. In this Communication, we describe the fabrication of low‐cost, high‐performance, digital nonvolatile memory devices based on semiconducting polymers, poly(o‐anthranilic acid) and poly(o‐anthranilic acid‐co‐aniline). These memory devices have ground‐breaking and novel current–voltage switching characteristics. The devices are switchable in a very low voltage range (which is much less than those of all other devices reported so far) with a very high ON/OFF current ratio (which is on the order of 10⁵). The low critical voltages have the advantage for nonvolatile memory device applications of low operation voltages and hence low power consumption. With this very low power consumption, the devices demonstrate in air ambient to have very stable ON‐ and OFF‐states without any degradation for a very long time (which has been confirmed up to one year so far) and to be repeatedly written, read and erased. Our study proposes that the ON/OFF switching of the devices is mainly governed by a filament mechanism. The high ON/OFF switching ratio and stability of these devices, as well as their repeatable writing, reading and erasing capability with low power consumption, opens up the possibility of the mass production of high performance digital nonvolatile polymer memory devices with low cost. Further, these devices promise to revolutionize microelectronics by providing extremely inexpensive, lightweight, and versatile components that can be printed onto plastics, glasses or metal foils.     

Non‐volatile Ferroelectric Poly(vinylidene fluoride‐co‐trifluoroethylene) Memory Based on a Single‐Crystalline Tri‐isopropylsilylethynyl Pentacene Field‐Effect Transistor

A new type of nonvolatile ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) memory based on an organic thin‐film transistor (OTFT) with a single crystal of tri‐isopropylsilylethynyl pentacene (TIPS‐PEN) as the active layer is developed. A bottom‐gate OTFT is fabricated with a thin P(VDF‐TrFE) film gate insulator on which a one‐dimensional ribbon‐type TIPS‐PEN single crystal, grown via a solvent‐exchange method, is positioned between the Au source and drain electrodes. Post‐thermal treatment optimizes the interface between the flat, single‐crystalline ab plane of TIPS‐PEN and the polycrystalline P(VDF‐TrFE) surface with characteristic needle‐like crystalline lamellae. As a consequence, the memory device exhibits a substantially stable source–drain current modulation with an ON/OFF ratio hysteresis greater than 10³, which is superior to a ferroelectric P(VDF‐TrFE) OTFT that has a vacuum‐evaporated pentacene layer. Data retention longer than 5 × 10⁴ s is additionally achieved in ambient conditions by incorporating an interlayer between the gate electrode and P(VDF‐TrFE) thin film. The device is environmentally stable for more than 40 days without additional passivation. The deposition of a seed solution of TIPS‐PEN on the chemically micropatterned surface allows fabrication arrays of TIPS‐PEN single crystals that can be potentially useful for integrated arrays of ferroelectric polymeric TFT memory.     

Non‐Volatile Polymer Electroluminescence Programmable with Ferroelectric Field‐Induced Charge Injection Gate

Electroluminescence (EL) of organic and polymeric fluorescent materials programmable in the luminance is extremely useful as a non‐volatile EL memory with the great potential in the variety of emerging information storage applications for imaging and motion sensors. In this work, a novel non‐volatile EL memory in which arbitrarily chosen EL states are programmed and erased repetitively with long EL retention is demonstrated. The memory is based on utilizing the built‐in electric field arising from the remnant polarization of a ferroelectric polymer which in turn controls the carrier injection of an EL device. A device with vertically stacked components of a transparent bottom electrode/a ferroelectric polymer/a hole injection layer/a light emitting layer/a top electrode successfully emits light upon alternating current (AC) operation. Interestingly, the device exhibits two distinctive non‐volatile EL intensities at constant reading AC voltage, depending upon the programmed direct current (DC) voltage on the ferroelectric layer. DC programmed and AC read EL memories are also realized with different EL colors of red, green and blue. Furthermore, more than four distinguishable EL states are precisely addressed upon the programmed voltage input each of which shows excellent EL retention and multiple cycle endurance of more than 10⁵ s and 10² cycles, respectively.     

Self‐Powered Trace Memorization by Conjunction of Contact‐Electrification and Ferroelectricity

Triboelectric nanogenerator (TENG) is a newly invented technology that can effectively harvest ambient mechanical energy from various motions with promising applications in portable electronics, self‐powered sensor networks, etc. Here, by coupling TENG and a thin film of ferroelectric polymer, a new application is designed for TENG as a self‐powered memory system for recording a mechanical displacement/trace. The output voltage produced by the TENG during motion can polarize the dipole moments in the ferroelectric thin film. Later, by applying a displacement current measurement to detect the polarization density in the ferroelectric film, the motion information of the TENG can be directly read. The sliding TENG and the single‐electrode TENG matrix are both utilized for realizing the memorization of the motion trace in one‐dimensional and two‐dimensional space, respectively. Currently, the ferroelectric thin film with a size of 3.1 mm² can record a minimum area changing of 30 mm² and such resolution can still be possibly improved. These results prove that the ferroelectric polymer is an effective memory material to work together with TENG and thereby the fabricated memory system can potentially be used as a self‐powered displacement monitor.     

High‐Performance Organic Transistor Memory Elements with Steep Flanks of Hysteresis

High‐performance organic transistor memory elements with donor‐polymer blends as buffer layers are presented. These organic memory transistors have steep flanks of hysteresis with an ON/OFF memory ratio of up to 2 × 10⁴, and a retention time in excess of 24 h. Inexpensive materials such as poly(methyl methacrylate), ferrocene and copper phthalocyanine are used for the device fabrication, providing a convenient approach of producing organic memory transistors at low cost and high efficiency.     

Self‐Assembled Nanowires of Organic n‐Type Semiconductor for Nonvolatile Transistor Memory Devices

Organic nonvolatile transistor‐type memory (ONVM) devices are developed using self‐assembled nanowires of n‐type semiconductor, N,N′‐bis(2‐phenylethyl)‐perylene‐3,4:9,10‐tetracarboxylic diimide (BPE‐PTCDI). The effects of nanowire dimension and silane surface treatment on the memory characteristics are explored. The diameter of the nanowires is reduced by increasing the non‐solvent methanol composition, which led to the enhanced crystallinity and high field‐effect mobility. The BPE‐PTCDI nanowires with small diameters induce high electrical fields and result in a large memory window (the shifting of the threshold voltage, ΔV_th). The ΔV_th value of BPE‐PTCDI nanowire based ONVM device on the bare substrate can reach 51 V, which is significantly larger than that of thin film. The memory window is further enhanced to 78 V with the on/off ratio of 2.1 × 10⁴ and the long retention time (10⁴ s), using a hydrophobic surface (such as trichloro(phenyl)silane‐treated surface). The above results demonstrate that the n‐type semiconducting nanowires have potential applications in high performance non‐volatile transistor memory devices.     

Novel Rewritable,Non‐volatile Memory Devices Based on Thermally and Dimensionally Stable Polyimide Thin Films

Novel digital memory devices were fabricated with a thermally and dimensionally stable polyimide containing carbazole moieties in its side groups by using a simple and conventional solution coating process. The devices exhibit excellent unipolar ON and OFF switching behavior. With very low power consumption, the devices can be repeatedly written, read, and erased in air. The ON/OFF current ratio of the devices is high up to 10¹¹. The high ON/OFF switching ratio and stability of the devices, as well as their repeatable writing, reading, and erasing capability with low power consumption, open up the possibility of the mass production of high performance non‐volatile memory devices at low cost.     

High‐Performance Nonvolatile Transistor Memories of Pentacence Using the Green Electrets of Sugar‐based Block Copolymers and Their Supramolecules

Reported here are the nonvolatile electrical characteristics of pentacene‐based organic field‐effect transistor (OFET) memory devices created from the green electrets of sugar‐based block copolymer maltoheptaose‐block‐polystyrene (MH‐b‐PS), and their supramolecules with 1‐aminopyrene (APy). The very hydrophilic and abundant‐hydroxyl MH block is employed as a charge‐trapping site, while the hydrophobic PS block serves as a matrix as well as a tunneling layer. The orientation of the MH nanodomains could be well controlled in the PS matrix with random spheres, vertical cylinders, and ordered horizontal cylinders via increasing solvent annealing time, leading to different electrical switching characteristics. The electron‐trapping ability induced by the horizontal‐cylinder MH is stronger than those of the random‐sphere and vertical‐cylinder structures, attributed to the effective contact area. The electrical memory window of the device is further improved via the supramolecules of hydrogen‐bonding 1‐aminopyrene to the MH moieties of MH‐b‐PS for enhancing the hole‐trapping ability. The optimized device using the horizontal cylinders of the supramolecule electret exhibits the excellent memory characteristics of a wide memory window (52.7 V), retention time longer than 10⁴ s with a high ON/OFF ratio of >10⁵, and stable reversibility over 200 cycles. This study reveals a new approach to achieve a high‐performance flash memory through the morphology control of sugar‐based block copolymers and their supramolecules.     

Flexible Nonvolatile Transistor Memory Devices Based on One‐Dimensional Electrospun P3HT:Au Hybrid Nanofibers

A novel flexible nonvolatile flash transistor memory devices on polyethylene naphthalate (PEN) substrate using 1D electrospun nanofiber of poly(3‐hexylthiophene) (P3HT):gold nanoparticles (Au NPs) hybrid as the channel is presented. The Au NPs are functionalized with self‐assembled monolayer (SAM) of para‐substituted amino (Au‐NH₂), methyl (Au‐CH₃) or trifluoromethyl (Au‐CF₃) tail groups on the benzenethiol moiety. They are employed as localized charge traps across the nanofiber channel and program/erase the device towards low conductance (OFF)/high conductance (ON) states under the applied electrical field. With the low operation voltage of ±5 V, the hybrid nanofiber transistor memories exhibit a 3.5–10.6 V threshold voltage shifting and at least 10⁴ s data retention, with a minimum effect on ≈100 programmed/erased stress endurances. The dipoles of the SAM probably modify the work function of the Au NPs associated with the P3HT nanofiber channel and manifest the degree of negative threshold voltage shifting in an order of Au‐NH₂ > Au‐CH₃ > Au‐CF₃. The devices remain reliable and stable even under the bending conditions (radius: 5–30 mm) or 1000 repetitive bending cycles. The hybrid nanofiber can be used to obtain high‐performance digital nanoscale memories for flexible high density data storage devices.     

A Polymer‐Electrolyte‐Based Atomic Switch

Studies on a resistive switching memory based on a silver‐ion‐conductive solid polymer electrolyte (SPE) are reported. Simple Ag/SPE/Pt structures containing polyethylene oxide–silver perchlorate complexes exhibit bipolar resistive switching under bias voltage sweeping. The switching behavior depends strongly on the silver perchlorate concentration. From the results of thermal, transport, and electrochemical measurements, it is concluded that the observed switching originates from formation and dissolution of a silver metal filament inside the SPE film caused by electrochemical reactions. This is the first report of an electrochemical “atomic switch” realized using an organic material. The devices also show ON/OFF resistance ratios greater than 10⁵, programming speeds higher than 1 μs, and retention times longer than 1 week. These results suggest that SPE‐based electrochemical devices might be suitable for flexible switch and memory applications.     

Interface Modifications of InAs Quantum‐Dots Solids and their Effects on FET Performance

InAs nanocrystals field‐effect transistors with an ON/OFF ratio of 10⁵ are reported. By tailoring the interface regions in the active layer step‐by‐step, the evolution of the ON/OFF ratio can be followed from approximately 5 all the way to around 10⁵. The formation of a semiconducting solid from colloidal nanocrystals is achieved through targeted design of the nanocrystal–nanocrystal interaction. The manipulation characteristics of the nanocrystal interfaces include the matrix surrounding the inorganic core, the interparticle distance, and the order of nanocrystals in the 3D array. Through careful analysis of device characteristics following each treatment, the effect of each on the physical properties of the films are able to be verified. The enhanced performance is related to interparticle spacing, reduction in sub‐gap states, and better electronic order (lower σ parameter). Films with enhanced charge transport qualities retain their quantum‐confined characteristics throughout the procedure, thus making them useful for optoelectronic applications.     

Synthesis of Alternating Copolysiloxane with Terthiophene and Perylenediimide Derivative Pendants for Involatile WORM Memory Device

Alternating copolysiloxane with both electron donor terthiophene and electron acceptor perylenediimide derivative pendants (PTSi‐alt‐PDISi) is synthesized successfully. The polymer exhibits high decomposition and glass transition temperatures, good film‐forming ability, and high morphological stability. The estimated HOMO and LUMO energy levels of PTSi‐alt‐PDISi are –5.77 and –3.90 eV, respectively. The fabricated memory device with the configuration of ITO/PTSi‐alt‐PDISi/Au(Al) shows nonvolatile write‐once‐read‐many‐times (WORM) memory characteristics. Its turn‐on threshold voltage is 1.7 V, while its ON/OFF current density ratio is around 10⁴ in ambient atmosphere. The well‐defined memory property of PTSi‐alt‐PDISi is attributed to the transition of the pendant terthiophene and perylenediimide groups from the disoriented state to the ordered face‐to‐face conformation at the threshold voltage and the charge transfer interaction between pendent terthiophene donor and perylenediimide acceptor moieties, which are confirmed by XRD patterns and fluorescence emission measurement. This suggests that the new donor–acceptor polysiloxanes have potential applications in the field of memory devices.     

One‐Step All‐Solution‐Based Au–GO Core–Shell Nanosphere Active Layers in Nonvolatile ReRAM Devices

Nonvolatile resistive random‐access memory devices based on graphene‐oxide‐wrapped gold nanospheres (AuNS@GO) are fabricated following a one‐step room‐temperature solution‐process approach reported herein for the first time. The effect of the thickness of the GO layer (2, 5, and 7 nm) and the size of the synthesized AuNS (15 and 55 nm) are inspected. Reliable bistable switching is observed in the devices made from a flexible substrate and incorporating 5 and 7 nm thick GO‐wrapped AuNS, sandwiched between two metal electrodes. Current–voltage measurements show bipolar switching behavior with an ON/OFF ratio of 10³ and relatively low operating voltage (?2.5 V). The aforementioned devices unveil remarkable robustness over 100 endurance cycles and a retention of 10³ s. Conversely, a 2 nm thick GO layer is shown to be insufficient to allow current passage from the bottom to the top electrodes. The resistive switching mechanism is demonstrated by space charge trapped limited current due to the AuNS in AuNS@GO matrix. The proposed device and methodology herein applied are expected to be attractive candidates for future generation flexible memory devices.     

Light‐Responsive Ion‐Redistribution‐Induced Resistive Switching in Hybrid Perovskite Schottky Junctions

Hybrid Perovskites have emerged as a class of highly versatile functional materials with applications in solar cells, photodetectors, transistors, and lasers. Recently, there have also been reports on perovskite‐based resistive switching (RS) memories, but there remain open questions regarding device stability and switching mechanism. Here, an RS memory based on a high‐quality capacitor structure made of an MAPbBr₃ (CH₃NH₃PbBr₃) perovskite layer sandwiched between Au and indium tin oxide (ITO) electrodes is reported. Such perovskite devices exhibit reliable RS with an ON/OFF ratio greater than 10³, endurance over 10³ cycles, and a retention time of 10⁴ s. The analysis suggests that the RS operation hinges on the migration of charged ions, most likely MA vacancies, which reversibly modifies the perovskite bulk transport and the Schottky barrier at the MAPbBr₃/ITO interface. Such perovskite memory devices can also be fabricated on flexible polyethylene terephthalate substrates with high bendability and reliability. Furthermore, it is found that reference devices made of another hybrid perovskite MAPbI₃ consistently exhibit filament‐type switching behavior. This work elucidates the important role of processing‐dependent defects in the charge transport of hybrid perovskites and provides insights on the ion‐redistribution‐based RS in perovskite memory devices.     

Self‐Assembly of π‐Conjugated Amphiphiles: Free Standing,Ordered Sheets with Enhanced Mobility

Oligo(p‐phenylenevinylenes) (OPVs) with amphiphilic character are synthesized and their self‐assembly characteristics studied. Careful studies point at two morphologically different states of assemblies, with one being two dimensional sheets and the other as rolled tubes. This is also the first time that self‐assembled sheets are achieved for OPVs. Morphological and photo‐physical studies reveal a unique aggregate to aggregate transition between rolled tubes and two dimensional sheets, which is outlined as a more thermodynamic aggregate. The thermodynamic aggregate (2D sheet) is better ordered and consists of chromophores that are better excitonically coupled. The mobilities of these aggregates are also studied for a field effect transistor device and as expected sheets supersede rolled tubes by a couple of orders. More interestingly, the mobility values obtained for the well ordered chromophores in sheets is three orders higher than any other self‐assembled OPV previously reported. It is hypothesized that the better π interactions enforced by the amphiphilic design and the resultant supramolecular organization is a prime factor for such a remarkable rise in mobilities.     

A Graphene‐Based Vacuum Transistor with a High ON/OFF Current Ratio

A graphene‐based vacuum transistor (GVT) with a high ON/OFF current ratio is proposed and experimentally realized by employing electrically biased graphene as the electron emitter. The states of a GVT are switched by tuning the bias voltage applied to the graphene emitter with an ON/OFF current ratio up to 10⁶, a subthreshold slope of 120 mV dec^?1 and low working voltages of <10 V, exhibiting switching performances superior to those of previously reported graphene‐based solid‐state transistors. GVTs are fabricated and integrated using silicon microfabrication technology. A perfectly symmetric ambipolar device is achieved by integrating two GVTs, implying the potential of realizing vacuum integrated circuits based on GVTs. GVTs are expected to find applications in extreme environments such as high temperature and intense irradiation.