In this paper, recent progress of binary metal-oxide resistive switching random access memory (RRAM) is reviewed. The physical mechanism, material properties, and electrical characteristics of a variety of binary metal-oxide RRAM are discussed, with a focus on the use of RRAM for nonvolatile memory application. A review of recent development of large-scale RRAM arrays is given. Issues such as uniformity, endurance, retention, multibit operation, and scaling trends are discussed.

Metal–Oxide RRAM

This review article attempts to provide a comprehensive review of the recent progress in the so-called resistive random access memories (RRAMs) First, a brief introduction is presented to describe the construction and development of RRAMs, their potential for broad applications in the fields of nonvolatile memory, unconventional computing and logic devices, and the focus of research concerning RRAMs over the past decade Second, both inorganic and organic materials used in RRAMs are summarized, and their respective advantages and shortcomings are discussed Third, the important switching mechanisms are discussed in depth and are classified into ion migration, charge trapping/de-trapping, thermochemical reaction, exclusive mechanisms in inorganics, and exclusive mechanisms in organics Fourth, attention is given to the application of RRAMs for data storage, including their current performance, methods for performance enhancement, sneak-path issue and possible solutions, and demonstrations of 2-D and 3-D crossbar arrays Fifth, prospective applications of RRAMs in unconventional computing, as well as logic devices and multi-functionalization of RRAMs, are comprehensively summarized and thoroughly discussed The present review article ends with a short discussion concerning the challenges and future prospects of the RRAMs

Recent progress in resistive random access memories: Materials, switching mechanisms, and performance

Over the past 20 years, organic transistors have developed from a laboratory curiosity to a commercially viable technology. This critical review provides a short summary of several important aspects of organic transistors, including materials, microstructure, carrier transport, manufacturing, electrical properties, and performance limitations (200 references).

Organic thin-film transistors.

Optical transparency, tunable conducting properties and easy processability make metal oxides key materials for advanced optoelectronic devices. This Review discusses recent advances in the synthesis of these materials and their use in applications. Metal oxides (MOs) are the most abundant materials in the Earth's crust and are ingredients in traditional ceramics. MO semiconductors are strikingly different from conventional inorganic semiconductors such as silicon and III–V compounds with respect to materials design concepts, electronic structure, charge transport mechanisms, defect states, thin-film processing and optoelectronic properties, thereby enabling both conventional and completely new functions. Recently, remarkable advances in MO semiconductors for electronics have been achieved, including the discovery and characterization of new transparent conducting oxides, realization of p-type along with traditional n-type MO semiconductors for transistors, p–n junctions and complementary circuits, formulations for printing MO electronics and, most importantly, commercialization of amorphous oxide semiconductors for flat panel displays. This Review surveys the uniqueness and universality of MOs versus other unconventional electronic materials in terms of materials chemistry and physics, electronic characteristics, thin-film fabrication strategies and selected applications in thin-film transistors, solar cells, diodes and memories.

Metal oxides for optoelectronic applications

This article provides an overview on the recent development of solution processed organic, inorganic, and hybrid interfacial materials for bulk-heterojunction polymer solar cells. The introduction of proper interfacial materials to optimize the electronic and electrical properties between the interfaces of the light-harvesting active layer and the charge-collecting electrode has become an important criterion to improve the performance of polymer solar cells. The electronic processes at these interfaces play a critical role in determining the efficiency for photon-to-electricity conversion. An ideal interface requires the formation of Ohmic contact with minimum resistance and high charge selectivity to prevent charge carriers from reaching the opposite electrodes. For long-term stability of polymer solar cells, interfaces with matched surface energy are required to prevent interfacial dewetting and delamination. Several classes of interfacial materials including inorganic metal oxides, crosslinkable charge-transporting materials, conjugated polymer electrolytes, self-assembled functional molecules, and graphene-based materials are highlighted and the integration of these interfacial materials with new low bandgap polymers and fullerene derivatives as active materials in different device architectures is also discussed.

Recent advances in solution-processed interfacial materials for efficient and stable polymer solar cells

Improving performance of organic solar cells using amorphous tungsten oxides as an interfacial buffer layer on transparent anodes

Unipolar resistive switching devices are investigated for nonvolatile memory applications in a metal-insulator-metal structure in which the insulator layer is based on sol-gel-derived zinc oxide (ZnO) films prepared by a simple spin-coating process followed by thermal annealing. Fast programming ( les 50 ns) and a high off-to-on resistance ratio ( ges 104) is demonstrated. The influences on the switching behaviors according to the crystallinity of the ZnO films are studied as a function of the annealing temperature. In addition, the devices are fabricated on a flexible plastic substrate and exhibit excellent durability upon repeated bending tests, demonstrating their potential for flexible low-cost memory devices.

Resistive Switching Characteristics of Sol–Gel Zinc Oxide Films for Flexible Memory Applications

The fabrication of pressure sensors based on reduced graphene oxide (rGO) as the sensing material is challenging due to the intrinsic hydrophobic behavior of graphene oxide inks as well as the agglomeration of graphene oxide flakes after reduction. Hydrazine (a reducing agent) and a dual-component additive comprising benzisothiazolinone and methylisothiazolinone in appropriate proportion were used to synthesize a rGO ink with a hydrophilic nature. Utilizing this hydrophilic rGO ink mixed with multiwalled carbon nanotubes (MWNTs), a very simple, low-cost approach is demonstrated for the fabrication of a pressure sensor based on polyurethane (PU) foam coated with the MWNT–rGO ink (MWNT–rGO@PU foam). The MWNT–rGO@PU foam-based devices are shown to be versatile pressure sensors with the potential to detect both small-scale and large-scale movements. At low pressure (below 2.7 kPa, 50% strain), the formation of microcracks that scatter electrical charges results in a detectable increase in resistance suitable ...

Highly Exfoliated MWNT-rGO Ink-Wrapped Polyurethane Foam for Piezoresistive Pressure Sensor Applications.

An analysis of the difference in behavior of top and bottom contact organic thin film transistors using device simulation

A nonvolatile memory is demonstrated using a solution-processed sol-gel ZnO thin-film transistor (TFT) in which Ag nanoparticles are embedded as charge storage nodes at the insulator-ZnO interface. Its TFT transfer characteristics exhibit a large clockwise hysteresis that is proportional to the gate bias sweep range. Measurement of the threshold voltage shift versus the pulse width of gate bias reveals that the device can be programed or erased at a time scale of as short as 10−4 s. Retention of the initial memory window is measured to be 27% after 105 s and projected to last until 107 s.

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Dipti Gupta

Papers

Improving performance of organic solar cells using amorphous tungsten oxides as an interfacial buffer layer on transparent anodes

Resistive Switching Characteristics of Sol–Gel Zinc Oxide Films for Flexible Memory Applications

Highly Exfoliated MWNT-rGO Ink-Wrapped Polyurethane Foam for Piezoresistive Pressure Sensor Applications.

An analysis of the difference in behavior of top and bottom contact organic thin film transistors using device simulation

Nonvolatile memory based on sol-gel ZnO thin-film transistors with Ag nanoparticles embedded in the ZnO/gate insulator interface