Electrical Bistability Research Articles

Effects of buffer layer and thermal annealing on the performance of hybrid Cu2S/PVK electrically bistable devices

Hybrid organic/inorganic electrically bistable devices (EBDs) based on Cu2S/PVK nanocomposites have been fabricated by using a simple spin-coating method. An obvious electrical bistability is observed in the current-voltage (I-V) characteristics of the devices, and the presence of the buffer layer and the annealing process have an important effect on the enhancement of the ON/OFF current ratios. Different electrical conduction mechanisms are responsible for the charge switching of the devices in the presence and absence of the buffer layer.

Templating C60 on MoS2 Nanosheets for 2D Hybrid van der Waals p–n Nanoheterojunctions

C60 and single-layer MoS2 nanocomposites were facilely prepared via a combined solvent transfer and surface deposition (STSD) method by templating C60 aggregates on 2D MoS2 nanosheets to construct hybrid van der Waals heterojunctions. The electronic property of the hybrid nanomaterials was investigated in a direct charge transport diode device configuration of ITO/C60–MoS2 nanocomposites/Al; rewritable nonvolatile resistive switching with low SET/RESET voltage (∼3 V), high ON/OFF resistance ratio (∼4 × 103), and superior electrical bistability (>104 s) of a flash memory behavior was observed. This particular electrical property of C60–MoS2 nanocomposites, not possessed by either C60 or MoS2 nanosheets, was supposed to be due to the efficiently established C60/MoS2 p–n nanojunction, which controls the electron tunneling via junction barriers modulated by electric-field-induced polarization. Thus, our 2D templating method through STSD is promising to massively allocate van der Waals p–n heterojunctions in 2...

Quadrupolar (A-π-D-π-A) Tetra-aryl 1,4-Dihydropyrrolo[3,2-b]pyrroles as Single Molecular Resistive Memory Devices: Substituent Triggered Amphoteric Redox Performance and Electrical Bistability

A series of quadrupolar (A-π-D-π-A) tetra-aryl 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) derivatives synthesized are showcased as potential organic resistive memory (ORM) devices for the first time. The experimental observations coupled with density functional theory (DFT) calculations probe in detail the role of terminal substituent groups (p-NH2, p-Cl, p-CN, p-NO2, m-NO2) on the optical and electrical properties. Electrochemical studies reveal that the 3- and 4-dinitro derivatives form an unusual class of tetra-aryl DHPPs that exhibit intrinsic amphoteric redox behavior contrary to the literature reports. The bipolar nature within a single molecule was harnessed to design operational ORMs. Interestingly, the memory devices fabricated using the structural isomers exhibited dissimilar memory characteristics. While the p-NO2 derivative displays permanent Write Once Read Many times (WORM) memory, its meta-counterpart represents a behavior akin to rewriteable flash memory. The noticeably higher ON/OFF ratio (∼...

Improvement of reliability of polymer nanocomposite based transparent memory device by oxygen vacancy rich ZnO nanorods

Different weight percent (wt%) of Zinc Oxide (ZnO) nanorods, prepared by chemical route, are used into polymethylmethacrylate (PMMA) to fabricate organic bistable devices (OBDs). The devices utilize spin coated polymer nanocomopsite thin film, which exhibit electrical bistability and WORM characteristics in switching between high conductive (ON) and low conductive (OFF) states and it has been observed that along with ZnO nanorod concentration, oxygen vacancy content is also an important factor for the achievement of ON-OFF conductive states. The maximum ON/OFF current ratio is of the order of 5×103 for Al/ZnO nanorods:PMMA/ITO heterostructures with 0.5wt% of ZnO nanorods. Statistical results indicate that the operating stability of devices with high retention time of 103s. We demonstrate that the enhancement of memory parameters are controlled by the oxygen vacancies existed in the engineered ZnO nanorods. These native defects are credited as basis of resistive switching behaviour of the devices. By comparing the C–V curves to the current–voltage (I–V) curves, dielectric constant, electron mobility and oxide trap densities have been estimated.

Memory properties of Au nanoparticles prepared by tuning HAuCl4 concentration using low-temperature hydrothermal reaction

An organic memory device with embedded gold nanoparticles (AuNPs) as charge storage elements and polymethylsilsesquioxane (PMSSQ) as organic dielectric layer was fabricated in this work. The AuNPs were prepared using sacrificial hydrothermal reaction on Al template, and the effect of HAuCl4 on size of AuNPs was studied. Field-emission scanning electron microscopy confirmed the increase of particle size with the increase in HAuCl4 concentration. X-ray diffraction analysis confirmed the formation of AuNPs with face-centered cubic (FCC) structure. The electrical properties of the memory system were investigated using a semiconductor characterization system. Current–voltage analysis confirmed the nonvolatile electrical bistability behavior and charge transport mechanism. Capacitance–voltage measurement indicated a memory behavior with flatband voltage shift because the AuNPs trapped and stored charges in the device. The optimal memory properties of AuNPs embedded in PMSSQ were obtained for FCC-structured AuNPs grown in 0.010M HAuCl4, with a mixture of 82±5nm (area density, 1.3×1012m−2) and 42±7nm (area density, 2.7×1012m−2) grain sizes that produced the lowest switch ON voltage of 2.2V and highest flatband voltage of 2.6V.

Metal nanoparticle mediated space charge and its optical control in an organic hole-only device

We reveal the role of localized space charges in hole-only devices based on an organic semiconductor with embedded metal nanoparticles (MNPs). MNPs act as deep traps for holes and reduce the current density compared to a device without MNPs by a factor of 104 due to the build-up of localized space charge. Dynamic MNPs charged neutrality can be realized during operation by electron transfer from excitons created in the organic matrix, enabling light sensing independent of device bias. In contrast to the previous speculations, electrical bistability in such devices was not observed.

Heating-up Synthesis of MoS2 Nanosheets and Their Electrical Bistability Performance.

Molybdenum disulfide (MoS2) nanosheets were synthesized by using a simple heating-up approach, in which 1-dodecanethiol (DDT) was used not only as a sulfur source but also as the surface ligand. The sheet-like morphology was confirmed by the transmission electron microscopy (TEM) and atomic force microscopy (AFM) results, and the X-ray diffraction (XRD) patterns and Raman spectrum were employed to characterize the structure of the as-synthesized MoS2 nanosheets. The as-obtained MoS2 nanosheets blending with a polymer could be used to fabricate an electrically bistable device through a simple spin-coating method, and the device exhibited an obvious electrical bistability in the I-V curve. The charge transport of the device was discussed based on the organic electronic models.

Oxygen Effects on Performance of Electrically Bistable Devices Based on Hybrid Silver Sulfide Poly(N-vinylcarbazole) Nanocomposites.

An organic/inorganic bistable device is fabricated by using a simple spin-coating technique, in which the hybrid silver sulfide (Ag2S) poly(N-vinylcarbazole) (PVK) nanocomposite film is sandwiched between two electrodes. An obvious electrical hysteresis is observed in the current-voltage (I-V) curve of the device measured in the presence of different oxygen concentrations, and the magnitude of the electrical hysteresis is decreased with a decrease of the oxygen concentrations. The electrical bistability of the device exhibits a strong dependence on the oxygen concentrations, and the current variation of the OFF state is higher than that of the ON state with the gas atmosphere changing from N2 to air. Different theoretical models have been employed to describe the carrier transport mechanisms of the device in the OFF and ON states measured in different gas atmospheres on the basis of the experimental I-V results, and the carrier transport of the device in the ON state measured in air is very different from that measured in N2 and low O2 concentrations due to the participation of oxygen vacancies in the trapping and de-trapping processes of electrons into and out of the Ag2S/PVK heterointerface.

Optical and electrical properties of p-substituted-benzylidenemalononitrile thin films: Optoelectronic applications

A donor-bridge-acceptor type conjugated molecule has been successfully synthesized and characterized. The optical properties such as absorption, photoluminescence and electrical properties such as cyclic-voltammetry and J–V characteristic of p-substituted-benzylidenemalononitrile (BMN) thin films have been investigated. The BMN films shows a wide absorption in visible region, which makes it possible for application in OPV and OLED. The band gap energy of BMN thin film was obtained by experimental calculation from cyclic voltammetry. From the current–voltage characteristics, the electrical bistability in such films can be associated with a memory phenomenon. The obtained results of the materials have promising to be applicable for various optoelectronic applications.

Selective Metal-vapor Deposition on Organic Surfaces.

Selective metal-vapor deposition signifies that metal-vapor atoms are deposited on a hard organic surface, but not on a soft (low glass transition temperature, low Tg ) surface. In this paper, we introduce the origin, extension, and applications of selective metal-vapor deposition. An amorphous photochromic diarylethene film shows light-controlled selective metal-vapor deposition, which is caused by a large Tg change based on photoisomerization, but various organic surfaces, including organic crystal and polymers, can be utilized for achieving selective metal-vapor deposition. Various applications of selective metal-vapor deposition, including cathode patterning of organic light-emitting devices, micro-thin-film fuses, multifunctional diffraction gratings, in-plane electrical bistability for memory devices, and metal-vapor integration, have been demonstrated.

Electrical Bistable Characteristics of Organic Charge Transfer Complex for Memory Device Applications

In this work, the electrical bistability of an organic CT complex is demonstrated and the possible switching mechanism is proposed. 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and tetracyanoquinodimethane (TCNQ) are used as an organic donor and acceptor, respectively, and poly-methamethylacrylate (PMMA) is used as a polymeric matrix for spin-coating. A device with the Al/(<TEX>$Al_2O_3$</TEX>)/PMMA:BCP:TCNQ[1:1:0.5 wt%]/Al configuration demonstrated bistable and switching characteristics similar to Ovshinsky switching with a low threshold voltage and a high ON/OFF ratio. An analysis of the current-voltage curves of the device suggested that electrical switching took place due to the charge transfer mechanism.

Unipolar resistive switching in metal oxide/organic semiconductor non-volatile memories as a critical phenomenon

Diodes incorporating a bilayer of an organic semiconductor and a wide bandgap metal oxide can show unipolar, non-volatile memory behavior after electroforming. The prolonged bias voltage stress induces defects in the metal oxide with an areal density exceeding 1017 m−2. We explain the electrical bistability by the coexistence of two thermodynamically stable phases at the interface between an organic semiconductor and metal oxide. One phase contains mainly ionized defects and has a low work function, while the other phase has mainly neutral defects and a high work function. In the diodes, domains of the phase with a low work function constitute current filaments. The phase composition and critical temperature are derived from a 2D Ising model as a function of chemical potential. The model predicts filamentary conduction exhibiting a negative differential resistance and nonvolatile memory behavior. The model is expected to be generally applicable to any bilayer system that shows unipolar resistive switching.

Structure and Electrical Bistability of a New Inorganic/Organic Hybird Based on Copper Iodide Polymer and Ethyl Viologen: A Synergic Combination of Experimental and Theoretical Study

Structure and Electrical Bistability of a New Inorganic/Organic Hybird Based on Copper Iodide Polymer and Ethyl Viologen: A Synergic Combination of Experimental and Theoretical Study

Electrical Property Variations in Organic Bistable Devices Utilizing CdSe/CdS/ZnS Core-Shell-Shell Nanoparticle Layer Embedded in a Polystyrene Layer Due to an Inserted WO3 Layer.

Organic bistable devices (OBDs) based on CdSe/CdS/ZnS core-shell-shell nanoparticles embedded in a polystyrene (PS) layer with an inserted WO3 layer were fabricated by using the spin coating method and the thermal evaporation. The current density-voltage (J-V) curves for the Al/CdSe/CdS/ZnS core-shell-shell nanoparticles embedded in PS layer/WO3/ITO devices with different thicknesses of WO3 layers exhibited electrical bistabilities. Simulated J-V curves for the OBDs containing CdSe/CdS/ZnS core-shell-shell nanoparticles were in reasonable agreement with the experimental results. The simulated J-V characteristics for the OBDs at various trap densities utilizing the double Gaussian distribution showed that the current level decreased with increasing shallow trap density and that the transition voltage increased with increasing deep trap density.

In-plane electrical bistability of photochromic diarylethene/Cu composite film

Electrical bistability is an essential property for memory devices. We report here the in-plane electrical bistability of photochromic diarylethene (DAE)/Cu composite film, which is prepared by Cu vapor deposition on the DAE surface with a low glass-transition temperature. The low-current level around 10−8A was switched to a high-current level of ca. 10−4A at a low threshold voltage (Vth) in the first voltage sweep. Once this switching occurred, the high-current level was kept in the second voltage sweep, and electrical bistability was achieved for the in-plane current. Vth was distributed in a wide range of voltages (0.5–10V), and the colored sample obtained by the UV irradiation showed a relatively higher Vth than the colorless sample. The highest ON–OFF ratio in current was ca. 106. The origin of the bistability attributed to the electrical breakdown in the insulated lines that was consisted of DAE in Cu film. The in-plane bistability of the DAE/Cu composite film has good retention time (>60min) and readout-cycle endurance (>106 cycles), indicating that it is suitable for write-once organic semiconductor memory characteristics.

Construction of RNA-Quantum Dot Chimera for Nanoscale Resistive Biomemory Application.

RNA nanotechnology offers advantages to construct thermally and chemically stable nanoparticles with well-defined shape and structure. Here we report the development of an RNA-QD (quantum dot) chimera for resistive biomolecular memory application. Each QD holds two copies of the pRNA three-way junction (pRNA-3WJ) of the bacteriophage phi29 DNA packaging motor. The fixed quantity of two RNAs per QD was achieved by immobilizing the pRNA-3WJ with a Sephadex aptamer for resin binding. Two thiolated pRNA-3WJ serve as two feet of the chimera that stand on the gold plate. The RNA nanostructure served as both an insulator and a mediator to provide defined distance between the QD and gold. Immobilization of the chimera nanoparticle was confirmed with scanning tunneling microscopy. As revealed by scanning tunneling spectroscopy, the conjugated pRNA-3WJ-QD chimera exhibited an excellent electrical bistability signal for biomolecular memory function, demonstrating great potential for the development of resistive biomolecular memory and a nano-bio-inspired electronic device for information processing and computing.

The Storage Cell Circuit with Memristor Characteristics of Poly(N-Vinylcarbazole) Films**Supported by the China Postdoctoral Science Foundation under Grant No 2011M50070.

A kind of non-conjugated polymer memory material, poly(N-vinylcarbazole), is used to investigate silicon-based storage performance with the fact that the one-bit storage cell circuit consists of a sandwiched indium-tinoxide/poly(N-vinylcarbazole)/Al and an n-type metal-oxide-semiconductor field effect transistor. The memristor on the basis of a nano poly(N-vinylcarbazole) film exhibits electrical bistability and flash memory features, for which the switching-on voltage is −1 V and the on/off current ratio approaches 104. At ambient temperature, the memory circuit possesses higher reliability within the programming time 104 s. The output voltage is close to 0.5 V during logic 1, while it is approximately 14 mV in the logic 0. This paves the way for the study on the technology concerning the binary encoding and data storage of nonvolatile memories.

Electrical Bistability and Erasable Memory Effect of a Functional Polyimide Film: Synthesis and Investigation of Mechanism

A functional polyimide (PI) film, (hexafluoroisopropylidene)diphthalic anhydride–2-(9H-carbazol-9-yl)ethyl 3,5-diaminobenzoate (6FDA–DADBC), in which DADBC serves as electron donor and 6FDA as electron acceptor, was synthesized in this work. The PI has electrical bistability and the sandwich device ITO‖6FDA–DADBC–PI‖Au made by using this functional PI as the active layer has nonvolatile memory-storage properties. It can be changed between the insulating state (Off state) and the conducting state (On state) by application of potentials of approximately 0.5 V and −2.5 V, respectively, with an On/Off current ratio of approximately 102, which is suitable for use as flash memory. Mechanisms of the charge transfer occurring in the materials were investigated, and are thoroughly discussed on the basis of molecular simulation. The PI has good thermal stability up to 400°C.

Electrically Driven Random Laser Memory

The first electrically driven random laser diode with nonvolatile resistive random access memory functionality is designed and demonstrated. To illustrate the working principle, a metal–insulator–semiconductor structure based on Pt/MgO/ZnO thin‐film layers is fabricated on indium tin oxide glass. The current–voltage curve of the dual‐function random laser memory (RLM) device exhibits an excellent electrical bistability with a high ON/OFF current ratio (≈107). The random lasing behavior is simultaneously demonstrated by using electrical pumping with the appearance of sharp‐peak emissions and a drastic enhancement of peak intensity. A wide angle‐dependent electroluminescence not only reveals its emitting advantage but also further supports the origin of random lasers. The first proof‐of‐concept presentation of RLM possesses several advantages of dual memory and lasing functions, which enables to open up new avenues to practical applications, such as light emitting memories for electrical and optical communication. This new horizon for the realization of all optical memories should therefore be able to attract academic as well as industrial interests. It is stressed here that the electrical reading of conventional memory array is usually in serial sequence, which limits the maximum data throughput. This hurdle can be overcome by optically readable memory devices.

Nonvolatile memory and opto-electrical characteristics of organic memory devices with zinc oxide nanoparticles embedded in the tris(8-hydroxyquinolinato)aluminum light-emitting layer

The nonvolatile organic memory devices based on the tris(8-hydroxyquinolinato)aluminum (Alq3) emitting layer embedded with zinc oxide nanoparticles (ZnO-NPs) are reported. The devices have a typical tri-layer structure consisting of the Alq3/ZnO-NPs/Alq3 layers interposed between indium tin oxide (ITO) and aluminum (Al) electrodes. An external bias is used to program the ON and OFF states of the device that are separated by a four-orders-of-magnitude difference in conductivity. No significant degradation of the device is observed in either the ON or OFF state after continuous stress (∼105s) and multicycle (∼103 cycles) testings. These nanoparticles behave as the charge trapping units, which enable the nonvolatile electrical bistability when biased to a sufficiently high voltage. Impedance spectroscopy, capacitance–voltage (C–V) and current–voltage (I–V) analysis are used to verify the possible physical mechanism of the switching operation. Moreover, it is found that the location of the ZnO-NPs could affect the memory and opto-electrical characteristics of the devices, such as the ON/OFF ratio, threshold voltage and turn-on voltage, which can be attributed to the influence of the ZnO-NPs and diffused Al atoms in the bulk of the Alq3 layer.