Organic Semiconductor Devices with Enhanced Field and Environmental Responses for Novel Applications
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Semiconductor Devices with Enhanced Field and Environmental Responses for Novel Applications
Takao Someya, Bholanath Pal, Jia Huang, and Howard E. Katz Abstract We discuss some recent advances in the use of organic semiconductor devices with additional or enhanced functionality beyond simple electrical switching. These include diodes that act as local temperature sensors or that filter reverse-bias currents at tens of megahertz frequency. Transistors are described with a range of sensing and reporting functions, for such properties as pressure, magnetic field, and chemical vapor. Because these devices will likely be employed in arrays and assemblies, we also present concepts of some larger, integrated components such as artificial skin, sensor arrays, and wireless power systems. The common theme of these devices is that they build on an extensive and growing understanding of the parent transistors and diodes, but represent a departure into new physical phenomena and application areas.
Introduction Organic semiconductor (OSC) fieldeffect transistors and diodes are a major topic of research in a wide range of settings, and a few are in initial phases of scale up and commercialization. Applications are in circuit elements ranging from individual pixels in display backplanes with one to six organic field-effect transistors (OFETs) to radio-frequency identification (RFID) circuits with thousands of OFETs and often diodes as well. Electronics based on printable and largely organic conductors, dielectrics, and semiconductors, with OFETs as the core devices, have become a research area in
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their own right and have spurred significant investment by established and emerging companies.1–4 Work on OFETs has been extensively reviewed,3,5–8 most notably and comprehensively in Chemistry of Materials, Materials Today, and Journal of Materials Research special issues.8–13 Several monographs have also been assembled, with representation from dozens of major research organizations.14–16 (Also see the article by Sirringhaus et al. in this issue.) The OFET is a three-terminal device in which one electrode, the gate, acts as a switching or controlling electrode to
define the conduction along a film of OSC between the other two electrodes, the source and the drain. The controlling mechanism is the creation of a layer of electrons or holes in the OSC film. The diode, on the other hand, is a twoterminal device that exhibits greater conductivity when voltage is applied in one direction than in the opposite direction and thereby can convert alternating current to direct current. The basis for such a device is the barrier in a semiconductor/semiconductor p–n junction or a metal/semiconductor Schottky contact, as has been demonstrated in many previous studies. The conductivity asymmetry arises because of differences in energy levels of charge carriers in the materials that meet at the junction. Often, holes are injected into one side of a diode and electrons into the other. The most fully developed OSC technology is in fact a diode, th
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