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

A new inelastic electron tunneling spectrometer with an absolute peak intensity is described. A smoothed second differential calculation is directly applied to high precision (7.5 digits) tunneling current‐voltage data measured with Al/AlOx/Benzoic Acid/Pb tunnel junctions at 4.2 K. Interpolation and accumulation in addition to the above calculation permit high resolution and high signal‐to‐noise ratio inelastic electron tunneling (IET) spectra with absolute intensities. The half width at half maximum is 22 cm−1 and signal‐to‐noise ratio is more than 26 at 1598 cm−1 at the smoothing parameter M=19. The absolute peak intensities of tunnel junctions doped with solutions of different concentrations are measured easily and simply with this new method. The absolute peak intensities increase with an increase in both the solution concentration and dipping time. This method shows promise as a quantitative surface analytic system.

New inelastic electron tunneling spectrometer with an absolute peak intensity

PURPOSE:To obtain a high performance polymer semiconductor element with stability and a method of manufacturing the same by using the surface of a copolymer which mainly contains poly-trimethyl-thiophene or trimethyl-thiophene formed on an electrode substrate as a bonding surface. CONSTITUTION:An example of a polymer semiconductor element is formed with a thin copolymer film which mainly has polytrimethyl-thiophene or trimethyl-thiophene formed on an electrode substrate 3, an upper electrode 1 made of indium formed on a semiconductor element 2, and further leads 4 are connected with the electrode 1 and the substrate 3. The polymer semiconductor thin film 2 uses the surface of the copolymer which mainly contains poly-trimethyl-thiophene or trimethyl-thiophene. The substrate polymerized with this trimethyl-thiophene includes, for example, one or more thiophene monomers such as thiophene. A method of manufacturing the copolymer which mainly contains the polymethyl-thiophene or trimethyl-thiophene is not limited.

Polymer semiconductor element and manufacture thereof

Electrical properties of I2-doped polydiacetylene

The conductance of trans‐polyacetylene is measured during oxidation using an interdigital microelectrode. The measurements obtained indicate a slight increase in the conductivity during initial exposure in air and then a decrease during oxidation, which is confirmed by the corresponding changes in the infrared absorption spectra. The logarithm of conductivity is inversely proportional to the oxidation time. A proposed model which is derived from Kivelson’s theory predicts the behavior of conductivity as a function of time during oxidation. The experimental data of conductivity is in agreement with the calculated data using this model. The temperature dependence of the conductivity at certain stages also supports the theory that the electrical transport mainly occurs through intersoliton electron hopping. Thus, the electrical transport mechanism during oxidation is clarified.

Fumihiro Ebisawa

Papers

Electrical properties of polyacetylene/polysiloxane interface

New inelastic electron tunneling spectrometer with an absolute peak intensity

Polymer semiconductor element and manufacture thereof

Electrical properties of I2-doped polydiacetylene

Conductance changes in trans‐polyacetylene during oxidation