The sequential block copolymerization of 4,4′-vinylphenyl-N,N-bis(4-tert-butylphenyl)benzenamine (A) with 2-(2-(4-vinylphenyl)ethynyl)pyridine (B) was simply carried out using only potassium naphthalenide (K-Naph) as an initiator without any additives in tetrahydrofuran (THF) at −78 °C. The well-defined functional block copolymers containing A block as an electron donor and B block as a weak electron acceptor had predictable molecular weights (Mn = 8,800–14,500 g/mol) and narrow molecular weight distributions (Mw/Mn = 1.09–1.10). The bicontinuous microphase-separated film morphology of the precisely synthesized poly(B-b-A-b-B) (PBAB) with 0.71 of fpoly(A), formed by thermal annealing at 230 °C for 9 h, was expected to be a potential active layer for nonvolatile memory device applications. Indium tin oxide (ITO)/PBAB/aluminum (Al) memory devices with an 8 × 8 cross-bar array structure exhibited nonvolatile resistive switching characteristics. The memory devices showed reliable memory performance in terms of ON/OFF ratios of ∼104, endurance cycles and retention time, and statistical data with regard to cumulative probability of the switching currents and threshold voltage distribution. Filamentary conduction mechanism was proposed to explain the switching of PBAB-based memory devices. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 2625-2632

We fabricated an 8×8 cross-bar array-type organic nonvolatile memory devices on twistable poly(ethylene terephthalate) (PET) substrate. A composite of polyimide (PI) and 6-phenyl-C61 butyric acid methyl ester (PCBM) was used as the active material for the memory devices. The organic memory devices showed a high ON/OFF current ratio, reproducibility with good endurance cycle, and stability with long retention time over 5×104s on the flat substrate. The device performance remained well under the twisted condition with a twist angle up to ∼30°. The twistable organic memory device has a potential to be utilized in more complex flexible organic device configurations.

In the above-named article [ibid., vol. 34, no. 1, pp. 51-53, Jan. 2013], the corresponding authors were not clearly specified. This correction is to indicate that Gun-Young Jung and Takhee Lee are the corresponding authors for the paper.

We demonstrated nonvolatile 8 × 8 array organic memory devices utilizing a PC-interface memory cell tester. The organic memory devices composed of a Ag/poly(3-hexylthiophene-2,5-diyl) (P3HT)/p + poly-Si structure exhibited excellent memory performance properties, including stable switching behavior, proper statistical distribution, and long retention time. We succeeded in independently addressing and reading the data in the memory cell array using the PC-interface memory cell tester, opening an avenue toward more realistic organic memory device applications.

Flexible materials and devices could be exploited in light-emitting diodes 1 , electronic circuits 2 , 3 , memory devices 4 , sensors 5 , 6 , displays 7 , 8 , solar cells 9 and bioelectronic devices 10 . Nanoscale elements such as thin films 11 , 12 , nanowires 13 , nanotubes 14 and nanoparticles 4 can also be incorporated into the active films of mechanically flexible devices. Large-area devices containing extremely thin films of molecular materials 15 , 16 represent the ultimate scaling of flexible devices based on organic materials, but the influence of bending and twisting on the electrical and mechanical stability of such devices has never been examined. Here, we report the fabrication and characterization of two-terminal electronic devices based on self-assembled monolayers of alkyl or aromatic thiol molecules on flexible substrates. We find that the charge transport characteristics of the devices remain stable under severe bending conditions (radius ≤ 1 mm) and a large number of repetitive bending cycles (≥1,000). The devices also remain reliable in various bending configurations, including twisted and helical structures.

We demonstrate the application of conventional photolithography to fabricate organic memory devices in an array structure with a cell area of 4 x 4 mu m(2) without damaging the underlying organic memory layer. Applying photolithography to organic electronic devices is not trivial because the solvents used during lithography may dissolve and damage the previously coated organic layers. The application of photolithography to our organic devices was possible because of the introduction of polymethyl methacrylate (PMMA)/polyvinyl alcohol (PVA) onto the memory active layer, where PMMA functions as a buffer layer to prevent dissolution of the PVA layer during developing process, and PVA acts as a striped layer during metal lift-off process. Embedded Al bottom electrodes were particularly constructed to minimize the switching failure. The completed organic memory devices exhibited typical unipolar switching behavior and excellent memory performance in terms of their statistical memory parameters (ON and OFF currents and threshold voltages), ON/OFF ratio (>10(2)), endurance (>230 cycles), and retention (>10(4) s). This convenient photolithography patterning technique is applicable for the further scaling of many types of organic devices. (C) 2011 Elsevier B.V. All rights reserved.

We fabricated an array-type organic nonvolatile memory device with multilayer graphene (MLG) film embedded in polyimide (PI) layers. The memory devices showed a high ON/OFF ratio (over 106) and a long retention time (over 104 s). The switching of the Al/PI/MLG/PI/Al memory devices was due to the presence of the MLG film inserted into the PI layers. The double-log current–voltage characteristics could be explained by the space-charge-limited current conduction based on a charge-trap model. A conductive atomic force microscopy found that the conduction paths in the low-resistance ON state were distributed in a highly localized area, which was associated with a carbon-rich filamentary switching mechanism.

Jae-Suk Lee, Takhee Lee, and co-workers investigate on page 385. structural and electrical characteristics of synthesized block copolymers consisting of poly(9-(4-vinylphenyl)carbazole)-b-poly(2-vinylpyridine) Various morphologies such as spherical or lamellar structures with microphase separation are obtained. In particular, devices with a lamellar structure exhibited memory switching, which is strongly related to the formation and rupture of highly conductive paths consisting primarily of carbazole segments.

The effect of active-area scale-down and improved memory performance of solution-processed TiO_x were investigated using devices with active areas ranging from 50 × 50 m2 to 200 × 200 nm2. As the active area decreases, higher operation voltages were required owing to the reduction of unintended extrinsic defects resulting from solution processing. Moreover, faster switching speeds were observed with decreasing active area, which is induced by incremental Joule heating. These scale-down effects provided enhanced reliability characteristics such as highly uniform operation voltages and resistance states and improved pulse endurance by minimizing extrinsic defect-related nonuniformity and introducing additional heating-assisted filamentary switching.

Electronic devices based on a series of synthesized block copolymers are demonstrated. In particular, a block copolymer system with a lamellar structure exhibits unipolar switching behavior. This study provides a simple strategy based on the adjustment of the block ratio in block copolymers to control the polymer morphology and thus the electrical and switching properties of polymer-based memory devices.

We report on the development of one‐diode and one‐resistor (1D‐1R) hybrid‐type devices consisting of inorganic Schottky diodes and organic unipolar memory, demonstrating electrically rewritable switching in the 1D‐1R system. The 1D‐1R array architecture improves the sensing efficiency of the array memory cell, ultimately creating the possibility for high‐density integrated organic memory devices without restrictions due to cross‐talk between cells.

We demonstrated unipolar organic bistable memory devices with 8 x 8 cross-bar array type structure. The active material for the organic non-volatile memory devices is poly(styrene-co-styrenesulfonic acid Na) (PSSANa). From the electrical measurements of the PSSANa organic memory devices, we observed rewritable unipolar switching behaviors with a stable endurance and narrow cumulative probability. Also the PSSANa memory devices exhibited a uniform cell-to-cell switching with a high ON/OFF ratio of approximately 10(5) and good retention time of approximately 10(4) seconds without significant degradation.

The organic memory device was fabricated 8 × 8 cross-bar array-type with transparent graphene electrodes on a poly(ethylene terephthalate) (PET) substrate. The active layer of the memory devices is a composite of polyimide and 6-phenyl-C61 butyric acid methyl ester (PCBM). The sheet resistance of the graphene film on memory device was found to be ∼270Ω/□, and the transmittance of separated graphene film from memory device was ∼92 %. The memory devices showed typical write-once-read-many (WORM) characteristics and an ON/OFF ratio of over ∼106. The memory devices also exhibited outstanding cell-to-cell uniformity with flexibility. There was no substantial variation observed in the current levels of the WORM memory devices upon bending and bending cycling up to 10,000 times. A retention time of over 104 sec was observed without fluctuation under bending.

Solution-processed TiOx layer was investigated as a candidate for next-generation resistive random access memory (ReRAM) application. TiOx active layer was prepared by simple spin coating process of a titanium(IV) isopropoxide precursor using sol-gel chemistry. Through the introduction of indium-tin-oxide (ITO) coated glass and polyethersulfone (PES) substrates. tranparent and flexible ReRAM devices were demonstrated, respectively. In addition, using scalable via-hole structure with nano-scale active area, the feasibility for high-density memory application was investigated. All ReRAM devices formed using various substrates exhibited good memory performance, such as stable dc I-V, ac endurance, and retention characteristics during maintaining their own unique functions accomplished by substrate properties. (C) 2011 Elsevier B.V. All rights reserved.

We demonstrate bipolar switching of organic resistive memory devices consisting of Ag/polymer/heavily-doped p-type poly Si junctions in an 8 x 8 cross-bar array structure. The bistable switching mechanism appears to be related to the formation and rupture of highly conductive paths, as shown by a direct observation of Ag metallic bridges using transmission electron microscopy and energy-dispersive X-ray spectroscopy. Current images of high-and low-conducting states acquired by conducting atomic force microscopy also support this filamentary switching mechanism. The filamentary formation can be described by an electrochemical redox reaction model of Ag. Our results may also be applied to other kinds of organic materials presenting similar switching properties, contributing to the optimization of device scaling or memory performance improvement.

We fabricated write-once-read-many times (WORM) type organic memory devices in 8 x 8 cross-bar structure. The active material for organic based WORM memory devices is mixture of both poly(4-vinyphenol) (PVP) and Vulcan XC-72s. From the electrical characteristics of the WORM memory devices, we observed two different resistance states, low resistance state and high resistance state, with six orders of ON/OFF ratio (I(ON)/I(OFF) - 10(6)). In addition, the WORM memory devices were maintained for longer than 50000 seconds without any serious degradation.

We fabricated 8 × 8 cross-bar array-type flexible organic resistive memory devices with transparent multilayer graphene (MLG) electrodes on a poly(ethylene terephthalate) substrate. The active layer of the memory devices is a composite of polyimide and 6-phenyl-C61 butyric acid methyl ester. The sheet resistance of the MLG film on memory device was found to be ∼270 Ω/◻, and the transmittance of separated MLG film from memory device was ∼92%. The memory devices showed typical write-once-read-many (WORM) characteristics and an ON/OFF ratio of over ∼10(6). The memory devices also exhibited outstanding cell-to-cell uniformity with flexibility. There was no substantial variation observed in the current levels of the WORM memory devices upon bending and bending cycling up to 10 000 times. A retention time of over 10(4) s was observed without fluctuation under bending.

We demonstrated a flexible resistive random access memory (FReRAM) device using a solution-processed TiOx active layer with an Al top electrode on an Ag layer-inserted indium-zinc-tin-oxide (IAI)-coated polyethersulfone substrate (Al/TiOx/IAI). Its feasibility of FReRAM application was evaluated through the comparison of electrical and mechanical characteristics with devices having different structure such as Ag/TiOx/Ag, Al/TiOx/indium-tin-oxide, and Al/TiOx/Al. As a result, our FReRAM device exhibited greater FReRAM performance such as stable memory characteristics under mechanically bent conditions and robustness to repetitive bending cycles. In addition, the device was thermally stable up to 85 °C, despite its flexible electrode and polymer substrate.

We propose a solution-processed transparent TiOx-based resistive switching random access memory (ReRAM) device. Electronically active TiOx was prepared by sol-gel spin coating of a titanium(IV) isopropoxide precursor on an indium tin oxide-coated glass. The prepared TiOx film is completely transparent in the visible range and has an amorphous structure. The fabricated TiOx-based ReRAM device exhibits distinct resistive switching under consecutive dc voltage sweeps of +/- 2 V. The device also exhibits good memory performance, including fast switching speed with a pulse width of 1 mu s, stable pulse endurance over 1000 cycles, and excellent retention characteristics at up to 125 degrees C. In addition, based on the log I - log V plot and X-ray photoelectron spectroscopy analysis, we postulate that the fabricated device is operated by the reversible formation/rupture of the conducting filament in the oxygen-deficient TiOx layer. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3489370] All rights reserved.