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

2.2. Materials 929 2.3. Factors Influencing Charge Mobility 931 2.3.1. Molecular Packing 931 2.3.2. Disorder 932 2.3.3. Temperature 933 2.3.4. Electric Field 934 2.3.5. Impurities 934 2.3.6. Pressure 934 2.3.7. Charge-Carrier Density 934 2.3.8. Size/molecular Weight 935 3. The Charge-Transport Parameters 935 3.1. Electronic Coupling 936 3.1.1. The Energy-Splitting-in-Dimer Method 936 3.1.2. The Orthogonality Issue 937 3.1.3. Impact of the Site Energy 937 3.1.4. Electronic Coupling in Oligoacene Derivatives 938

Charge transport in organic semiconductors.

Printed electronics is a revolutionary technology aimed at unconventional electronic device manufacture on plastic foils, and will probably rely on polymeric semiconductors for organic thin-film transistor (OTFT) fabrication. In addition to having excellent charge-transport characteristics in ambient conditions, such materials must meet other key requirements, such as chemical stability, large solubility in common solvents, and inexpensive solution and/or low-temperature processing. Furthermore, compatibility of both p-channel (hole-transporting) and n-channel (electron-transporting) semiconductors with a single combination of gate dielectric and contact materials is highly desirable to enable powerful complementary circuit technologies, where p- and n-channel OTFTs operate in concert. Polymeric complementary circuits operating in ambient conditions are currently difficult to realize: although excellent p-channel polymers are widely available, the achievement of high-performance n-channel polymers is more challenging. Here we report a highly soluble ( approximately 60 g l(-1)) and printable n-channel polymer exhibiting unprecedented OTFT characteristics (electron mobilities up to approximately 0.45-0.85 cm(2) V(-1) s(-1)) under ambient conditions in combination with Au contacts and various polymeric dielectrics. Several top-gate OTFTs on plastic substrates were fabricated with the semiconductor-dielectric layers deposited by spin-coating as well as by gravure, flexographic and inkjet printing, demonstrating great processing versatility. Finally, all-printed polymeric complementary inverters (with gain 25-65) have been demonstrated.

A high-mobility electron-transporting polymer for printed transistors

Organic-inorganic hybrid materials promise both the superior carrier mobility of inorganic semiconductors and the processability of organic materials A thin-film field-effect transistor having an organic-inorganic hybrid material as the semiconducting channel was demonstrated Hybrids based on the perovskite structure crystallize from solution to form oriented molecular-scale composites of alternating organic and inorganic sheets Spin-coated thin films of the semiconducting perovskite (C(6)H(5)C(2)H(4)NH(3))(2)SnI(4) form the conducting channel, with field-effect mobilities of 06 square centimeters per volt-second and current modulation greater than 10(4) Molecular engineering of the organic and inorganic components of the hybrids is expected to further improve device performance for low-cost thin-film transistors

https://science.sciencemag.org/content/sci/286/5441/945.full.pdf

Organic-inorganic hybrid materials as semiconducting channels in thin-film field-effect transistors

It is now widely accepted that skin sensitivity will be very important for future robots used by humans in daily life for housekeeping and entertainment purposes Despite this fact, relatively little progress has been made in the field of pressure recognition compared to the areas of sight and voice recognition, mainly because good artificial “electronic skin” with a large area and mechanical flexibility is not yet available The fabrication of a sensitive skin consisting of thousands of pressure sensors would require a flexible switching matrix that cannot be realized with present silicon-based electronics Organic field-effect transistors can substitute for such conventional electronics because organic circuits are inherently flexible and potentially ultralow in cost even for a large area Thus, integration of organic transistors and rubber pressure sensors, both of which can be produced by low-cost processing technology such as large-area printing technology, will provide an ideal solution to realize a practical artificial skin, whose feasibility has been demonstrated in this paper Pressure images have been taken by flexible active matrix drivers with organic transistors whose mobility reaches as high as 14 cm2/V·s The device is electrically functional even when it is wrapped around a cylindrical bar with a 2-mm radius

/pdf/a-large-area-flexible-pressure-sensor-matrix-with-organic-233vkpdvcr.pdf

A large-area, flexible pressure sensor matrix with organic field-effect transistors for artificial skin applications

The gate bias dependence of the field-effect mobility in pentacene-based insulated gate field-effect transistors (IGFETs) was interpreted on the basis of the interaction of charge carriers with localized trap levels in the band gap. This understanding was used to design and fabricate IGFETs with mobility of more than 0.3 square centimeter per volt per second and current modulation of 10 5 , with the use of amorphous metal oxide gate insulators. These values were obtained at operating voltage ranges as low as 5 volts, which are much smaller than previously reported results. An all-room-temperature fabrication process sequence was used, which enabled the demonstration of high-performance organic IGFETs on transparent plastic substrates, at low operating voltages for organic devices.

https://science.sciencemag.org/content/sci/283/5403/822.full.pdf

Low-Voltage Organic Transistors on Plastic Comprising High-Dielectric Constant Gate Insulators

Thin film transistors (TFT) comprising pentacene as the semiconductor layer and an amorphous metal oxide gate insulators with a dielectric constant around 16 were fabricated and tested. Field effect mobility values up to 0.6 cm/sup 2/ V/sup -1/ s/sup -1/ with subthreshold slopes up to 0.3 V/decade and current modulation higher than 10/sup 5/ were obtained at operating voltages ranging from 4 to 15 V. TFTs fabricated at room temperature on transparent plastic substrates and exhibiting similar transport characteristics were demonstrated.

J. Kymissis

Papers

Low-Voltage Organic Transistors on Plastic Comprising High-Dielectric Constant Gate Insulators

Organic transistors with low operating voltage and high mobility