Session L2: Organic and Molecular Bistability and Memory Devices

Organic electrical bistable devices and applications as electronic digital memory

Recently, organic electrical bistability has attracted considerable attention due to its potential applications as digital memory devices. In this presentation, we will present our recent study on organic electrical bistability phenomena and the application as nonvolatile memory devices (NVM). The bistability was discovered when a thin layer of metallic nano-particles introduced between two organic layers as the active cell, which interposed between two electrodes. We attribute this bistaility to the charge transfer and trap in the metal nano-particles. A further material engineering by dispersing metal nano-particles and organic electron donor within polymer films as the active cell, it forms the polymer-based memory devices. When the metal nanoparticles are integrated with tobacco mosaic virus as the active cell, it forms a virus-based (or bio-based) memory device. Mechanism studies on the polymer and bio-based memory device reveal that charge-storage in the metal nanoparticles plays an important role in the device operation. Details of the mechanism study and the memory device performance will be discussed in this presentation.   

Evaluation of switchable organic devices for nonvolatile memory applications

Many organic electronic devices exhibit switching behavior and have therefore been proposed as the basis for a nonvolatile memory technology. In particular, bistable resistive elements, in which a high or low current state is selected by application of a specific voltage, may be used as the elements of a crosspoint memory array. This architecture places very stringent requirements on the electrical response of the individual devices, in terms of on-state current density, switching and retention times, cycling endurance, rectification and size-scaling. In this talk, I will describe the progress that we and others have made towards satisfying these requirements. In many cases, the mechanisms responsible for conduction and switching are not fully understood. In some devices, it has been shown that current flows in a few highly localized regions. These so-called ``filaments'' are not necessarily metallic bridges between the electrodes, but may be associated with chains of nanoparticles introduced into the organic matrix either deliberately or accidentally. Coulomb blockade effects can then explain the switching behavior observed in some devices. \newline \newline This work was done in collaboration with L. D. Bozano, M. Beinhoff, K. R. Carter, V. R. Deline, B. W. Kean, G. M. McClelland, D. C. Miller, P. M. Rice, J. R. Salem, and S. A. Swanson.   

Controlling nanostructure in organic films to achieve high photovoltaic efficiency

We discuss the materials and device structures used to attain high efficiency organic solar cells based on small molecular weight organic thin films. The influence of structural morphology introduced using both vacuum thermal evaporation and organic vapor phase deposition in so-called bulk heterojunction and mixed molecular heterojunction cells is described. Furthermore, we describe the growth of all-organic nanostructures by organic vapor phase deposition to achieve very high solar energy conversion efficiencies. Many of these approaches have potential for resulting in solar power conversion efficiencies $>$10{\%}. In addition, materials and strategies for increasing the open circuit voltage, and to extend the sensitivity of organic solar cells out into the near infrared spectral region are discussed.   

Large-Scale Molecular and Nanoelectronic Circuits \& Associated Opportunities

According to the International Technology Roadmap for Semiconductors (ITRS), by year 2020 it is expected that the most closely spaced metallic wires within a DRAM circuit will be patterned at a pitch of about 30 nm, implying that the conductors themselves will be of a width of around 15 nm. However, virtually every aspect of achieving this technology is considered to be `red,' meaning that there is no known solution. Nevertheless, ultra-high density (semiconductor and metallic) nanowire circuitry, fabricated at 2020 dimensions and beyond, would be expected to provide a host of value traditional (logic \& memory) and nontraditional (sensing, thermoelectrics, etc.) functions. In this talk we will discuss the fabrication and testing of large scale circuitry ($>$ 10$^5$ devices) aimed a these various applications. This will include a 160,000 bit memory circuit that is no larger than a white blood cell, high-performance, ultra-dense \& energy efficient logic circuitry, nanowire sensing arrays, and high-performance silicon-based thermoelectric devices. We will also discuss how these circuits may be fabricated on a host of substrates, including plastic.