Search

The electronic device, with its biocompatibility, biodegradability, and ease of fabrication process, shows great potential to embed into health monitoring and hardware data security systems. Herein, polyvinylpyrrolidone (PVP) biopolymer is presented as an active layer, electrochemically active magnesium (Mg) as a metal electrode, and chitosan‐based substrate (CHS) to fabricate biocompatible and biodegradable physically transient neuromorphic device (W/Mg/PVP/Mg/CHS). The I–V curve of device is non‐volatile bipolar in nature and shows a unique compliance‐induced multilevel RESET‐dependent‐SET behavior while sweeping the compliance current from a few microamperes to milliamperes. Non‐volatile and stable switching properties are demonstrated with a long endurance test (100 sweeps) and retention time of over 104 s. The physically transient memristor (PTM) has remarkably high dynamic RON/ROFF (ON/OFF state resistance) ratio (106 Ω), and when placed in deionized (DI) water, the device is observed to completely dissolve within 10 min. The pulse transient measurements demonstrate the neuromorphic computation capabilities of the device in the form of excitatory post synaptic current (EPSC), potentiation, depression, and learning behavior, which resemble the biological function of neurons. The results demonstrate the potential of W/Mg/PVP/Mg/CHS device for use in future healthcare and physically transient electronics. [ABSTRACT FROM AUTHOR]

The development and application of artificial intelligence have led to the exploitation of low‐power and compact intelligent information‐processing systems integrated with sensing, memory, and neuromorphic computing functions. The 2D van der Waals (vdW) materials with abundant reservoirs for arbitrary stacking based on functions and enabling continued device downscaling offer an attractive alternative for continuously promoting artificial intelligence. In this study, full 2D SnS2/h‐BN/CuInP2S6 (CIPS)‐based ferroelectric field‐effect transistors (Fe‐FETs) and utilized light‐induced ferroelectric polarization reversal to achieve excellent memory properties and multi‐functional sensing‐memory‐computing vision simulations are designed. The device exhibits a high on/off current ratio of over 105, long retention time (>104 s), stable cyclic endurance (>350 cycles), and 128 multilevel current states (7‐bit). In addition, fundamental synaptic plasticity characteristics are emulated including paired‐pulse facilitation (PPF), short‐term plasticity (STP), long‐term plasticity (LTP), long‐term potentiation, and long‐term depression. A ferroelectric optoelectronic reservoir computing system for the Modified National Institute of Standards and Technology (MNIST) handwritten digital recognition achieved a high accuracy of 93.62%. Furthermore, retina‐like light adaptation and Pavlovian conditioning are successfully mimicked. These results provide a strategy for developing a multilevel memory and novel neuromorphic vision systems with integrated sensing‐memory‐processing. [ABSTRACT FROM AUTHOR]

This study focuses on InGaZnO-based synaptic devices fabricated using reactive radiofrequency sputtering deposition with highly uniform and reliable multilevel memory states. Electron trapping and trap generation behaviors were examined based on current compliance adjustments and constant voltage stressing on the ITO/InGaZnO/ITO memristor. Using O2 + N2 plasma treatment resulted in stable and consistent cycle-to-cycle memory switching with an average memory window of ~95.3. Multilevel resistance states ranging from 0.68 to 140.7 kΩ were achieved by controlling the VRESET within the range of −1.4 to −1.8 V. The modulation of synaptic weight for short-term plasticity was simulated by applying voltage pulses with increasing amplitudes after the formation of a weak conductive filament. To emulate several synaptic behaviors in InGaZnO-based memristors, variations in the pulse interval were used for paired-pulse facilitation and pulse frequency-dependent spike rate-dependent plasticity. Long-term potentiation and depression are also observed after strong conductive filaments form at higher current compliance in the switching layer. Hence, the ITO/InGaZnO/ITO memristor holds promise for high-performance synaptic device applications. [ABSTRACT FROM AUTHOR]

Abstract The development and application of artificial intelligence have led to the exploitation of low‐power and compact intelligent information‐processing systems integrated with sensing, memory, and neuromorphic computing functions. The 2D van der Waals (vdW) materials with abundant reservoirs for arbitrary stacking based on functions and enabling continued device downscaling offer an attractive alternative for continuously promoting artificial intelligence. In this study, full 2D SnS2/h‐BN/CuInP2S6 (CIPS)‐based ferroelectric field‐effect transistors (Fe‐FETs) and utilized light‐induced ferroelectric polarization reversal to achieve excellent memory properties and multi‐functional sensing‐memory‐computing vision simulations are designed. The device exhibits a high on/off current ratio of over 105, long retention time (>104 s), stable cyclic endurance (>350 cycles), and 128 multilevel current states (7‐bit). In addition, fundamental synaptic plasticity characteristics are emulated including paired‐pulse facilitation (PPF), short‐term plasticity (STP), long‐term plasticity (LTP), long‐term potentiation, and long‐term depression. A ferroelectric optoelectronic reservoir computing system for the Modified National Institute of Standards and Technology (MNIST) handwritten digital recognition achieved a high accuracy of 93.62%. Furthermore, retina‐like light adaptation and Pavlovian conditioning are successfully mimicked. These results provide a strategy for developing a multilevel memory and novel neuromorphic vision systems with integrated sensing‐memory‐processing.

Abstract The electronic device, with its biocompatibility, biodegradability, and ease of fabrication process, shows great potential to embed into health monitoring and hardware data security systems. Herein, polyvinylpyrrolidone (PVP) biopolymer is presented as an active layer, electrochemically active magnesium (Mg) as a metal electrode, and chitosan‐based substrate (CHS) to fabricate biocompatible and biodegradable physically transient neuromorphic device (W/Mg/PVP/Mg/CHS). The I–V curve of device is non‐volatile bipolar in nature and shows a unique compliance‐induced multilevel RESET‐dependent‐SET behavior while sweeping the compliance current from a few microamperes to milliamperes. Non‐volatile and stable switching properties are demonstrated with a long endurance test (100 sweeps) and retention time of over 104 s. The physically transient memristor (PTM) has remarkably high dynamic RON/ROFF (ON/OFF state resistance) ratio (106 Ω), and when placed in deionized (DI) water, the device is observed to completely dissolve within 10 min. The pulse transient measurements demonstrate the neuromorphic computation capabilities of the device in the form of excitatory post synaptic current (EPSC), potentiation, depression, and learning behavior, which resemble the biological function of neurons. The results demonstrate the potential of W/Mg/PVP/Mg/CHS device for use in future healthcare and physically transient electronics.

The emergence of 2D wide-bandgap semiconductor (WBGS) GeSe2 as charge-trapping dielectrics has helped realize superior devices by using an extremely simple device setup. However, the controllability of deep-gap-state defects in 2D GeSe2 poses a challenge due to the vulnerability and susceptibility of charge-trapping centers, resulting in various problems, i.e., small memory window and poor device durability during programming. Herein, we deliberately perform asymmetric interfacial oxidation to reinforce the memory performance based on the WSe2/Janus-GeSe2 van der Waals heterostructure, which exhibits a giant memory window ratio of 88.5% (70.8 V at ±40 V gate sweep range), high-room-temperature hole mobility of 15 cm2 V–1 s–1, and low nonlinearity factor close to 0 with regard to synaptic weight update characteristics. The information storage performance is excellent, owing to the interface rendered by asymmetric oxidation in the GeSe2 layer, providing an effective charge-trapping layer and atomically flat surface to enhance the mobility of the WSe2 channel. The controllable strategy helps to derive a simple design principle to realize high-performance 2D WBGS GeSe2-based memory and electrical synaptic devices with complex neural functions. [ABSTRACT FROM AUTHOR]

The development of field‐effect transistor‐based (FET‐based) non‐volatile optoelectronic memories is vital toward innovations necessary to improve computer systems. In this work, for the first time, the unique charge‐trapping and charge‐retention properties of solution‐processed colloidal nitrogen‐doped carbon quantum dots (CQDs) are harnessed to achieve functional optoelectronic memories programmable by UV illumination with a multilevel writing possibility. Of particular note, long‐lasting memory function can be achieved thanks to the vast charge trapping sites provided by the N‐doped CQDs and the resultant photo‐gating effect is exercised on the graphene FET. The achieved memory can be erased by a positive gate bias which provides sufficient carriers to remove trapped charges through recombination. This study highlights the possibility to engineer high‐performance all‐carbon non‐volatile FET‐based optoelectronic memories through manipulating and coupling the charge‐trapping properties of colloidal CQDs and graphene. [ABSTRACT FROM AUTHOR]

Abstract The development of field‐effect transistor‐based (FET‐based) non‐volatile optoelectronic memories is vital toward innovations necessary to improve computer systems. In this work, for the first time, the unique charge‐trapping and charge‐retention properties of solution‐processed colloidal nitrogen‐doped carbon quantum dots (CQDs) are harnessed to achieve functional optoelectronic memories programmable by UV illumination with a multilevel writing possibility. Of particular note, long‐lasting memory function can be achieved thanks to the vast charge trapping sites provided by the N‐doped CQDs and the resultant photo‐gating effect is exercised on the graphene FET. The achieved memory can be erased by a positive gate bias which provides sufficient carriers to remove trapped charges through recombination. This study highlights the possibility to engineer high‐performance all‐carbon non‐volatile FET‐based optoelectronic memories through manipulating and coupling the charge‐trapping properties of colloidal CQDs and graphene.

A series of (CH3NH 3) 2- x Cs x AgBiBr 6 films (x =0, 0.1, 0.2, 0.3, 0.4) were fabricated on ITO/glass substrates through the sol-gel method. 15 % Cs doping (x =0.3) was the optimal condition for enhancing the film quality and achieving nonvolatile bipolar resistive switching (BRS) performance in the devices. The on/off ratio in the (CH 3 NH 3) 1.7 Cs 0.3 AgBiBr 6 (Cs-MAABB-3)-based RS device reached 7.7×104, high and low resistance states were maintained for over 104 s. Under different light intensities with a wavelength of 430 nm, six distinct resistance states were recorded at −0.3 V in the Au/Cs-MAABB-3/ITO/glass device. These multilevel states remained after 5000 s and 650 cycles, indicating the excellent retention and endurance of multilevel RS memory in the Au/Cs-MAABB-3/ITO/glass device. The RS behavior in this device followed the trap-controlled space charge-limited current and conductive filament models. Cs-doping increased the concentration of intrinsic vacancies appropriately, leading to a more prominent RS effect. With varying intensities of illumination, the change of Schottky-like barrier at the Au/Cs-MAABB-3 interface, modulated by the photo-induced carriers, affected the multilevel resistance states in the device. The excellent multilevel RS performance was observed for the first time in the Cs-MAABB-3-based device. It presents broad possibilities for improving high-density memory in lead-free halide double perovskite-based devices. [Display omitted] • The 15% Cs-doping at the A-site could improve the flatness and density of (CH 3 NH 3) 2 AgBiBr 6 (MAABB) film. • Retention, endurance and the ON/OFF ratio in the 15% Cs doped MAABB (Cs-MAABB-3)-based RS memory were enhanced substantially. • Six levels of resistance states were exhibited in the Au/Cs-MAABB-3/ITO/glass device with different intensities of light. •.RS behavior was controlled by SCLC and CF models in the Cs-MAABB-3 layer under optical and electric fields. •.Reversible change in the Schttky barrier at the Au/Cs-MAABB-3 interface was also attributed to the RS behavior under light. [ABSTRACT FROM AUTHOR]

Spin‐orbit torque (SOT) promises fast and reliable switching of the perpendicular magnetization in spintronic devices, such as magnetic random‐access memory or spin logic devices. To apply the SOT technology to practical devices with low power consumption, it is necessary to reduce the switching current. To this end, most of the research to date in this area has focused on improving the charge‐to‐spin conversion efficiency in heavy metal/ferromagnet structures. In this study, it is reported that the SOT switching current is significantly reduced by modulating magnetic easy‐cone states through voltage‐controlled magnetic anisotropy (VCMA). The introduction of a thin Pt layer at the CoFeB/MgO interface enhances the VCMA effect, allowing a magnetic easy‐cone state of CoFeB to be formed and controlled by the gate voltage. As a result, the SOT switching current density is reduced by up to 50% when the easy‐cone angle is changed from 0° to 58°. Furthermore, the magnetic easy‐cone state is gradually modulated in a reversible and non‐volatile manner, facilitating multilevel spintronic devices. [ABSTRACT FROM AUTHOR]

Direct charge trapping memory, a new concept memory without any dielectric, has begun to attract attention. However, such memory is still at the incipient stage, of which the charge‐trapping capability depends on localized electronic states that originated from the limited surface functional groups. To further advance such memory, a material with rich hybrid states is highly desired. Here, a van der Waals heterostructure design is proposed utilizing the 2D graphdiyne (GDY) which possesses abundant hybrid states with different chemical groups. In order to form the desirable van der Waals coupling, the plasma etching method is used to rapidly achieve the ultrathin 2D GDY with smooth surface for the first time. With the plasma‐treated 2D GDY as charge‐trapping layer, a direct charge‐trapping memory based on GDY/MoS2 is constructed. This bilayer memory is featured with large memory window (90 V) and high degree of modulation (on/off ratio around 8 × 107). Two operating mode can be achieved and data storage capability of 9 and 10 current levels can be obtained, respectively, in electronic and opto‐electronic mode. This GDY/MoS2 memory introduces a novel application of GDY as rich states charge‐trapping center and offers a new strategy of realizing high performance dielectric‐free electronics, such as optical memories and artificial synaptic. [ABSTRACT FROM AUTHOR]

Abstract Direct charge trapping memory, a new concept memory without any dielectric, has begun to attract attention. However, such memory is still at the incipient stage, of which the charge‐trapping capability depends on localized electronic states that originated from the limited surface functional groups. To further advance such memory, a material with rich hybrid states is highly desired. Here, a van der Waals heterostructure design is proposed utilizing the 2D graphdiyne (GDY) which possesses abundant hybrid states with different chemical groups. In order to form the desirable van der Waals coupling, the plasma etching method is used to rapidly achieve the ultrathin 2D GDY with smooth surface for the first time. With the plasma‐treated 2D GDY as charge‐trapping layer, a direct charge‐trapping memory based on GDY/MoS2 is constructed. This bilayer memory is featured with large memory window (90 V) and high degree of modulation (on/off ratio around 8 × 107). Two operating mode can be achieved and data storage capability of 9 and 10 current levels can be obtained, respectively, in electronic and opto‐electronic mode. This GDY/MoS2 memory introduces a novel application of GDY as rich states charge‐trapping center and offers a new strategy of realizing high performance dielectric‐free electronics, such as optical memories and artificial synaptic.

Sneak path current generated by adjacent cells in three-dimensional (3D) memristor arrays must be curbed while securing the multi-bit storage capability of each cell to aid in the cost-effective increase in array size. For this purpose, a 3D stackable TaOx/HfO2-based selectorless memristor has been proposed and optimized via capacitance-dependent voltage division analysis. The proposed device utilizes the formation or rupture of conductive filaments for self-rectifying resistive switching operation, in contrast to nonfilamentary devices that often exploit the change in the charge state of the electron trap. This approach enables the reduction of the trapped charge leakage through the interface between the resistive switching and metal layers effectively, giving rise to excellent retention properties (>5 × 105 s). Furthermore, the proposed device exhibits a sufficiently high on/off ratio (~1.35 × 103), rectification ratio (~2.3 × 103), endurance (1.5 × 102 cycles), and low resistance variation (standard deviation

Deep ultraviolet (DUV) light monitoring has a wide range of applications in areas such as military surveillance, biological/medical analysis, and flame detection. In this paper, a novel nonvolatile solar‐blind DUV photoelectric memory is investigated based on an organic field effect transistor (OFET). It has 16 different optical memory states of multilevel memory behavior and rewriting capability. The memory window of the device reaches to 23.8 V under a gate voltage of −40 V and 254 nm (DUV) illumination (1.252 mW cm–2). Moreover, the device has a retention time of over 104 s, more than 100 cycles of writing/reading/erasing/reading (W/R/E/R), and an ION/IOFF ratio of about 102. The memory behavior can be modulated via the gate voltage, light intensity, and exposure time. In addition, determination of the exposure dose to DUV light is achieved. The memory shows a highly selectivity, which is sensitive to 254 nm DUV. Furthermore, a DUV memory array is fabricated, and the image processing and storage capabilities are verified. This novel device shows a promising path toward highly (wavelength) selective and advanced multilevel solar‐blind DUV monitors. [ABSTRACT FROM AUTHOR]

Abstract The Pt/CeO 2 /Nb:SrTiO 3 heterostructure that exhibits excellent resistive switching (RS) behavior of a maximum RS ratio of 3 × 104, good retention and multilevel memory is prepared. Obvious photoresponse was observed in this device under the illumination of a laser beam of 405 nm wavelength, which exhibits significant switching characteristics at high resistance state. Both light-controlled RS and voltage-controlled photoresponse are demonstrated in this device. Such RS and photoresponse characteristics can be attributed to the Schottky barrier of Pt/CeO 2 interface and the electrons trapping/detrapping by oxygen vacancies near the interface. Our work demonstrated feasibility for making multilevel RS memories and for use in multifunctional photoelectric sensors. Highlights • Pt/CeO 2 /NSTO heterostructures show excellent RS and multilevel memory characteristics. • The heterostructure has significant switching photoresponse at high resistance state. • Both light-controlled RS and voltage-controlled photoresponse are demonstrated. • The excellent properties are attributed to interface barrier and oxygen vacancies. • Show applications in multilevel RS memories and multifunctional photoelectric sensors. [ABSTRACT FROM AUTHOR]

Abstract: The molecular stacking in film state has been confirmed to have an important influence on electronic properties of organic semiconductors. Thus, how to improve the molecular stacking and the corresponding device performance through molecular design is a difficult question that researches want to figure out. In this work, three small molecules with different bridge‐spacers, phenyl ring, pyridine, and pyrimidine, are designed to study the effect of nitrogen amount on molecular stacking in film state. The infrared spectroscopy in solution and film states are first measured to consider the hydrogen bond between the neighboring molecules, which can induce ordered molecular stacking through intermolecular interaction. X‐ray diffraction, atomic force microscopy, and grazing incidence small angle X‐ray scattering measurements confirm the ordered molecular stacking and crystalline orientation of nitrogenous heterocycles substituted molecules in film state. Additionally, nitrogenous heterocycles substituted molecules exhibit the excellent ternary data‐storage properties with low threshold voltage and high current ratio. This result presents the strategy for designing novel small molecules with excellent molecular stacking in film state. [ABSTRACT FROM AUTHOR]

Summary: In this work, the benefits of memristor‐based multilevel memories are described along with their design problems. Starting with measurements of discrete actual devices, a discrete memristor‐based multilevel memory is developed. It uses a printed circuit board in order to connect eight packaged memristors from Bio Inspired to test a ternary arithmetic logic unit on a field programmable gate array. These circuits are then integrated in the second proposed memory system based on a 150‐nm CMOS process that can be equipped with memristors on top of the metal layers. This integrated solution includes proper read‐out, erase, and write circuits to control real memristors and 32×32 memristive memory cells. It is compared with a common static random‐access memory in terms of area, computation speed, and power consumption showing benefits for memory sizes bigger than 70 words. Because yield and device variations are still a big issue in memristor fabrication, methods to counter these problems are also proposed in the end. An actual implementation should offer several trimming solutions to ensure proper functionality of a prototype memory as well as a power‐on calibration, until these problems are solved. The development of the presented memories is not only based on different models but also based on measurements done with real devices. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Improving organic devices via molecular design is challenging and difficult to rationalize because individual molecular properties always convolute with intermolecular interaction and crystallinity to contribute the device performance. In this work, it is demonstrated for the first time that racemic effect can be utilized to effectively improve memory device performance. A pair of enantiomers and their mixture are used to prepare organic multilevel resistive random access memory (RRAM) devices. The RRAM devices fabricated from the equimolar mixture of enantiomers are of the lowest onset voltages and highest ternary device yield, independent of the preparation methods. Structural analysis of the powder, film, and single crystal of the equimolar mixture reveals formation of a real racemic compound, where π–π stacking in contrast to the only C–H–π interaction in the film of pure enantiomers appears. Since individual enantiomer has identical electronic properties, the discrepancy in device performance is attributed to the different intermolecular interactions. [ABSTRACT FROM AUTHOR]

Memristor based crossbar memories are prime candidates to succeed the Flash as the mainstream nonvolatile memory due to their density, scalability, write endurance and capability of storing multibit per cell. In this paper, we present a memristor crossbar memory architecture that utilizes a reduced constraint read-monitored-write scheme. The proposed scheme supports multibit storage per cell and utilizes reduced hardware, aiming to decrease the feedback complexity and latency while still operating with CMOS compatible voltages. We additionally present a read technique that can successfully distinguish resistive states under the existence of resistance drift due to read/write disturbances in the array. We also provide derivations of analytical relations to set forth a design methodology in selecting peripheral device parameters. [ABSTRACT FROM PUBLISHER]

This paper proposes a multilevel memory circuit with a simple structure composed of two oxide thin film transistors (Ox-TFTs) and one capacitor. The proposed memory circuit utilizes low leakage current characteristics of the Ox-TFT. Simulation and measurement results confirm that the proposed memory circuit can achieve multilevel memory feature. [ABSTRACT FROM AUTHOR]

Broad spectral response and high photoelectric conversion efficiency are key milestones for realizing multifunctional, low-power optoelectronic devices such as artificial synapse and reconfigurable memory devices. Nevertheless, the wide bandgap and narrow spectral response of metal-oxide semiconductors are problematic for efficient metal-oxide optoelectronic devices such as photonic synapse and optical memory devices. Here, a simple titania (TiO 2 )/indium-gallium-zinc-oxide (IGZO) heterojunction structure is proposed for efficient multifunctional optoelectronic devices, enabling widen spectral response range and high photoresponsivity. By overlaying a TiO 2 film on IGZO, the light absorption range extends to red light, along with enhanced photoresponsivity in the full visible light region. By implementing the TiO 2 /IGZO heterojunction structure, various synaptic behaviors are successfully emulated such as short-term memory/long-term memory and paired pulse facilitation. Also, the TiO 2 /IGZO synaptic transistor exhibits a recognition rate up to 90.3% in recognizing handwritten digit images. Moreover, by regulating the photocarrier dynamics and retention behavior using gate-bias modulation, a reconfigurable multilevel (≥8 states) memory is demonstrated using visible light., (© 2023 Wiley-VCH GmbH.)

Nanowire memristor devices that display multilevel memory effects are of great interest for high-density storage, however, numerous challenges remain in fabricating high-quality, stable memory units. A plasmonic-radiation-enhanced technique is introduced in this work for scalably forming nanowire multilevel memory units with superior properties. Femtosecond laser irradiation of gold-titanium dioxide nanowire-gold structures results in plasmonic-enhanced optical absorption in the TiO2 locally at the metal-oxide interface. This produces junctions with superior mechanical and electrical contact, and engineers a concentration of charged defects in the TiO2 near the interface, which enables stable multilevel memory behavior without the need for a traditional electroforming step. The memory units produced display eight-level current amplification under continuous forward voltage cycles, and can replicate complex multilevel memory sequences without interference between the different multilevel states. [ABSTRACT FROM AUTHOR]

A multilevel resistive-change memory device with thin-film transistor (TFT) structure is proposed, in which both functions of transistor and nonvolatile memory can be performed. Al-doped ZnO was employed for the active channel of the TFT as well as for the resistive-change material of the memory device. Multilevel memory operations could be realized by controlling the number of conducting filaments within the channel. Sound TFT characteristics and nonvolatile memory functions were demonstrated. The programmed current ratios for three-level memory states were 1:3.8:25. As results, long-time stability ( 10^4 s) and program endurance (100 cycles) for the three-level memory states were also confirmed. [ABSTRACT FROM PUBLISHER]

A novel multilevel resistive switching was observed in epoxy methacrylate resin (EMAR) and carbon nanotubes (CNTs) composite films fabricated by spin coating method. The fabricated devices demonstrated the rewritable nonvolatile memory characteristics. More significantly, the memory device based on EMAR+CNTs composite exhibits multilevel stable conductivity states with stable intermediate resistance states in response to the applied voltage. By setting different compliance current and content of CNTs in composite film, the multilevel ON-states and even the multilevel OFF-states have been observed in our memory device. As fabricated devices exhibited multilevel resistive switching with stable resistance ratio between different resistance states having good data retention and endurance characteristics. It offers a novel design strategy for solution processable multilevel data storage. [ABSTRACT FROM AUTHOR]

The practical application of organic memory devices requires low power consumption and reliable device quality. Herein, we report that inserting thienyl units into D-π-A molecules can improve these parameters by tuning the texture of the film. Theoretical calculations revealed that introducing thienyl π bridges increased the planarity of the molecular backbone and extended the D-A conjugation. Thus, molecules with more thienyl spacers showed improved stacking and orientation in the film state relative to the substrates. The corresponding sandwiched memory devices showed enhanced ternary memory behavior, with lower threshold voltages and better repeatability. The conductive switching and variation in the performance of the memory devices were interpreted by using an extended-charge-trapping mechanism. Our study suggests that judicious molecular engineering can facilitate control of the orientation of the crystallite in the solid state to achieve superior multilevel memory performance. [ABSTRACT FROM AUTHOR]

Two acceptor–donor–acceptor (A–D–A) type organic small molecules, 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis(N-(4-nitrophenyl)-N-phenylaniline) (NTPA 2 BT) and 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diylbis(ethyne-2,1-diyl))bis(N-(4-nitrophenyl)-N-phenylaniline) (NTPA 2 EBT), differing by an alkynyl bridge, were designed, synthesized and fabricated into resistive random access memory devices. Compared with NTPA 2 BT, the fabricated memory device based on NTPA 2 EBT of extra alkynyl bridges presents nonvolatile ternary memory performance with lower threshold voltages, better stability and higher reproducibility. X-ray diffraction (XRD) patterns show that the NTPA 2 EBT film is much more regularly crystallized. Meanwhile, the photophysical and electrochemical properties indicate that the insertion of conjugated bridges in molecular structures could help to improve data storage characteristics with lower power consumption. Our results show that alkynyl is an important group to tailor organic molecules to achieve excellent data storage devices. [ABSTRACT FROM AUTHOR]

For the organic memory device with vertically arranged electrodes, controlling the film-packing to achieve highly oriented crystallite arrangement is critical but challenging for obtaining the satisfied performance. Here, the effect of backbone planarity on the crystallite orientation is studied. Two diketopyrrolopyrrole-based small molecules (NI2PDPP and NI2FDPP) are synthesized with increasing planarity by furan substitution for phenyl rings. Upon thin-film analysis by atomic force microscopy, X-ray diffraction, and grazing-incidence small-angle X-ray scattering, the orientations of these crystallites are demonstrated to be well controlled through tailoring molecular planarity. The highly planar NI2FDPP in film prefers out-of-plane crystallite orientation with respect to the substrate normal while the nonplanar NI2PDPP displays less ordered packing with a broad orientation distribution relative to the substrate. As a result, NI2FDPP-based memory device exhibits superior multilevel performance. More importantly, the oriented crystallite arrangement favors uniformity in NI2FDPP thin film, thus, the device displays higher reproducibility of memory effects. This study provides an effective synthetic strategy for designing multilevel memory materials with favorable crystallite orientation. [ABSTRACT FROM AUTHOR]

In this work, we study charge trapping in floating-gate organic thin-film transistor nonvolatile memories (FG-OTFT-NVMs) fabricated by a simple method. The inner discrete distribution aluminum nanoparticles (Al-Nps) and the continuous compact thin alumina film were formed to act as the floating-gate and the tunneling dielectric layer, respectively by thermally evaporated Al at a slow rate and then heat annealed in dry air. The devices exhibited remarkable photoresponse and memory effect. Compared with the unidirectional threshold voltage ( V T ) shifts of memories by programming/erasing (P/E) in dark, larger bidirectional V T shifts were obtained by light-assisted programming, and therefore the memory performances were enhanced. A multilevel memory behavior was observed in our memories, which depended on programming conditions. The charge trapping mechanisms of memories operated in dark and under illumination are discussed, respectively. The results indicate that optimal memory performance requires charge carriers of both polarities, because it is a very efficient method to enlarge the memory window and to lower the P/E voltage by overwriting trapped charges by injected charges of opposite polarity. [ABSTRACT FROM AUTHOR]

A superior organic ternary write-once-read-many-times (WORM) memory was achieved by introducing alkynyl π bridges and tert -butyl substituent moieties onto the D-A-D molecular backbone, which enhance the field-induced intramolecular and intermolecular charge transfer (CT) effect, thereby contributing to the formation of the second conducting channel and realizing multilevel data storage. [Display omitted] • A new approach for multilevel storage through C–H···π, C–H···N interactions is reported. • Alkynyl π bridges and tBu groups are confirmed to be the origin of the second conducting channel from the single crystal structure of tBu-TEBT. • The logic gates and information display function based on tBu-TEBT device have been successfully accomplished for the first time. 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 (V th), 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 V th1 (1.6 V) and V th2 (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. [ABSTRACT FROM AUTHOR]

A new tetraazatetracene derivative, 2,3-[4,4'- bis(N,N-diphenylamino)benzyl]-5,12-bis[(triisopropylsilyl)ethynyl]- 1,4,6,11-tetraazatetracene (TPAs-BTTT), displays rewritable multilevel memory behavior, which is probably induced by multielectron intramolecular charge transfer (CT). [ABSTRACT FROM AUTHOR]

Polymer ferroelectric-gate field effect transistors (Fe-FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next-generation non-volatile memory. Furthermore, polymer Fe-FETs have been recently of interest owing to their capability of storing data in more than 2 states in a single device, that is, they have multi-level cell (MLC) operation potential for high density data storage. However, among a variety of technological issues of MLC polymer Fe-FETs, the requirement of high voltage for cell operation is one of the most urgent problems. Here, a low voltage operating MLC polymer Fe-FET memory with a high dielectric constant ( k) ferroelectric polymer insulator is presented. Effective enhancement of capacitance of the ferroelectric gate insulator layer is achieved by a simple binary solution-blend of a ferroelectric poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) ( k ≈ 8) with a relaxer high- k poly(vinylidene-fluoride-trifluoroethylene-chlorotrifluoroethylene) (PVDF-TrFE-CTFE) ( k ≈ 18). At optimized conditions, a ferroelectric insulator with a PVDF-TrFE/PVDF-TrFE-CTFE (10/5) blend composition enables the discrete six-level multi-state operation of a MLC Fe-FET at a gate voltage sweep of ±18 V with excellent data retention and endurance of each state of more than 104 s and 120 cycles, respectively. [ABSTRACT FROM AUTHOR]

Multilevel data memory and artificial synaptic plasticity in poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] ferroelectric field effect transistors were demonstrated. The dynamics of ferroelectric polarization transformation modulate potential of transistor channel, and adjust the electric field of the P(VDF-TrFE) ferroelectric film by potential along channel direction, thus realizing the multilevel nonvolatile memory state. The artificial synaptic plasticity of transistor is simulated, and the long-term plasticity of excited/inhibited postsynaptic current, paired impulse facilitation/inhibition, and spike-rate-dependent plasticity is realized. In long-term potentiation/depression simulation of devices, the conductivity symmetry and linearity are improved by setting the amplitude of the pulse increments. In addition, the vector-matrix multiplication operation was performed in a crossbar array. This work demonstrates the scheme to develop the P(VDF-TrFE) transistors-based multilevel memory and neural morphological computing. [Display omitted] • A programming scheme is proposed to modulate channel electric field. • The application of 3-bit/cell operation multilevel memory is illustrated. • The potential is modulated from polarization transformation dynamics. • Artificial synaptic plasticity of P(VDF-TrFE) FeFETs is simulated. • The conductivity symmetry and linearity are improved. [ABSTRACT FROM AUTHOR]

A continuum of stable remanent resistance states is reported in perpendicularly magnetized pseudo spin valves with a graded anisotropy free layer. The resistance states can be systematically set by an externally applied magnetic field. The gradual reversal of the free layer with applied field and the field-independent fixed layer leads to a range of stable and reproducible remanent resistance values, as determined by the giant magnetoresistance of the device. An analysis of first-order reversal curves combined with magnetic force microscopy shows that the origin of the effect is the field-dependent population of up and down domains in the free layer. [ABSTRACT FROM AUTHOR]

Recently acclaimed the fourth fundamental circuit element, the memristor was theoretically predicted by Leon Chua in 1971, although its single device electronic implementation eluded the attention of integrated circuit designers for the past three decades and was first reported in 2008 by the Hewlett-Packard (HP) Laboratory researchers while developing crossbar-based ultra high-density nonvolatile memories. Memristor-based hybrid nanoscale CMOS technology is expected not only to impact the flash memory industries profoundly, but also to revolutionize digital and neuromorphic computing. The memristor exhibits a dynamical resistance state that depends on its excitation history and which can be exploited to build transistor-less nonvolatile semiconductor memory (NVSM), commonly known as resistive RAM (RRAM). This paper addresses an implementation scheme for memristor-based resistive random access memory (MRRAM), a nano-scale binary memory that is compatible with modern computer systems. Its structure is similar to that of static random access memory (SRAM), but with the memristor replacing the underlying RS flip-flop. By improving the MRRAM, we propose a multilevel memory with greater data density, which stores multiple bit information in gray-scale form in a memory unit. Reported computer simulations and numerical analyses verify the effectiveness of the proposed scheme in storing ASCII characters and gray-scale images in binary format. [ABSTRACT FROM AUTHOR]