Organic thin-film transistors (OTFTs) have lived to see great improvements in recent years. This review presents new insight into conduction mechanisms and performance characteristics, as well as opportunities for modeling properties of OTFTs. The shifted focus in research from novel chemical structures to fabrication technologies that optimize morphology and structural order is underscored by chapters on vacuum-deposited and solution-processed organic semiconducting films. Finally, progress in the growing field of the n-type OTFTs is discussed in ample detail. The Figure, showing a pentacene film edge on SiO2, illustrates the morphology issue.

Organic Thin Film Transistors for Large Area Electronics

Electron and ambipolar transport in organic field-effect transistors.

Field-effect transistors based on solution-processible organic semiconductors have experienced impressive improvements in both performance and reliability in recent years, and printing-based manufacturing processes for integrated transistor circuits are being developed to realize low-cost, large-area electronic products on flexible substrates. This article reviews the materials, charge-transport, and device physics of solution-processed organic field-effect transistors, focusing in particular on the physics of the active semiconductor/dielectric interface. Issues such as the relationship between microstructure and charge transport, the critical role of the gate dielectric, the influence of polaronic relaxation and disorder effects on charge transport, charge-injection mechanisms, and the current understanding of mechanisms for charge trapping are reviewed. Many interesting questions on how the molecular and electronic structures and the presence of defects at organic/organic heterointerfaces influence the device performance and stability remain to be explored.

Device Physics of Solution‐Processed Organic Field‐Effect Transistors

In this paper we review recent progress in materials, fabrication processes, device designs, and applications related to organic thin-film transistors (OTFTs), with an emphasis on papers published during the last three years. Some earlier papers that played an important role in shaping the OTFT field are included, and a number of previously published review papers that cover that early period more completely are referenced. We also review in more detail related work that originated at IBM during the last four years and has led to the fabrication of high-performance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.

Organic thin-film transistors: a review of recent advances

The first solid‐state field‐effect transistor has been fabricated utilizing a film of an organic macromolecule, polythiophene, as a semiconductor. The device characteristics have been optimized by controlling the doping levels of the polymer. The device is a normally off type and the source (drain) current can be modulated by a factor of 102–103 by varying the gate voltage. The carrier mobility and the transconductance have also been determined to be ∼10−5 cm2/V s and 3 nS, respectively, by means of electrical measurements.

Macromolecular electronic device: Field-effect transistor with a polythiophene thin film

Polyacetylene/polysiloxane interface states have been investigated using metal‐insulator‐semiconductor (MIS) diodes. The 1‐mm2 MIS diodes (Al/polysiloxane/polyacetylene) have been fabricated by use of a conventional photolithographic technique. The I‐V and C‐V measurements were used to explore the polyacetylene/polysiloxane interface electrical properties. The electrical conduction mechanism in this interface was found to be a Schottky‐Richardson mechanism. Using the C‐V measurements to determine the interface states density distribution, it was found that the distribution had a U shape in the gap and its minimum value was 6×1013 eV−1 cm−2. An attempt was made to fabricate an insulating gate field‐effect transistor which worked as a depletion‐type transistor with a very low transconductance, gm =13 nΩ−1.

Electrical properties of polyacetylene/polysiloxane interface

Low loss plastic optical fibers (POF’s) have been prepared employing a poly(methylmethacrylate‐d8) core and fluorinated alkyl methacrylate copolymer cladding with attenuation losses of 20, 25, and 50 dB/km at wavelengths of 660, 780, and 850 nm, respectively. These values were attained using the POF fabrication method which incorporates a closed polymerization and fiber drawing procedure. The POF can allow optical signal transmission over about 1300 m at −34 dBm at a rate up to 10 MHz using a display grade GaAlAs light‐emitting diode whose emission power at 660 nm and 20 mA of forward input current is 1 mW. The loss limit of this poly(methylmethacrylate‐d8) core POF is estimated to be 10 dB/km at 680 nm.

Low loss poly(methylmethacrylate‐d8) core optical fibers

Low-loss plastic optical fibers

Low‐loss plastic optical fibers (POF) have been prepared with the attenuation loss of 114 dB/km at the wavelength of 670 nm employing polystylene core and ethylene‐vinylacetate copolymer cladding. The POF can allow the use for short‐distance optical signal transmission. The theoretical loss limit of polystylene core POF is calculated to be 70 dB/km at 670 nm.

https://library.naist.jp/dspace/bitstream/handle/10061/8595/JAppPhy_52_12_7061.pdf;sequence=1

Low-loss polystyrene core-optical fibers

In a sealed system, a polymerization initiator and a chain transfer agent are added to a methyl methacrylate monomer distilled under reduced pressure condition via a distillation step of the former both ingredients, the methyl methacrylate monomer is successively polymerized to prepare a core polymer while maintaining the reduced pressure condition, then the resulting core polymer is subjected to melt spinning to form a core fiber while maintaining the sealed system, and a clad of a macromolecular compound having a refractive index lower than that of the aforesaid core fiber is adhered around the periphery thereof, whereby a low-loss plastic optical fiber with excellent optical transmission characteristics having a core-cladding structure is fabricated. Plastic optical fibers so made exhibit light attenuation as low as 60 dB/km or lower.

Shigeo Nara

Papers

Electrical properties of polyacetylene/polysiloxane interface

Low loss poly(methylmethacrylate‐d8) core optical fibers

Low-loss plastic optical fibers

Low-loss polystyrene core-optical fibers

Fabrication of a low-loss plastic optical fiber