At present, flexible displays are an important focus of research. Further development of large, flexible displays requires a cost-effective manufacturing process for the active-matrix backplane, which contains one transistor per pixel. One way to further reduce costs is to integrate (part of) the display drive circuitry, such as row shift registers, directly on the display substrate. Here, we demonstrate flexible active-matrix monochrome electrophoretic displays based on solution-processed organic transistors on 25-microm-thick polyimide substrates. The displays can be bent to a radius of 1 cm without significant loss in performance. Using the same process flow we prepared row shift registers. With 1,888 transistors, these are the largest organic integrated circuits reported to date. More importantly, the operating frequency of 5 kHz is sufficiently high to allow integration with the display operating at video speed. This work therefore represents a major step towards 'system-on-plastic'.

There is ample evidence that organic field-effect transistors have reached a stage where they can be industrialized, analogous to standard metal oxide semiconductor (MOS) transistors. Monocrystalline silicon technology is largely based on complementary MOS (CMOS) structures that use both n-type and p-type transistor channels. This complementary technology has enabled the construction of digital circuits, which operate with a high robustness, low power dissipation and a good noise margin. For the design of efficient organic integrated circuits, there is an urgent need for complementary technology, where both n-type and p-type transistor operation is realized in a single layer, while maintaining the attractiveness of easy solution processing. We demonstrate, by using solution-processed field-effect transistors, that hole transport and electron transport are both generic properties of organic semiconductors. This ambipolar transport is observed in polymers based on interpenetrating networks as well as in narrow bandgap organic semiconductors. We combine the organic ambipolar transistors into functional CMOS-like inverters.

The scaling behavior of the transfer characteristics of solution-processed disordered organic thin-film transistors with channel length is investigated. This is done for a variety of organic semiconductors in combination with gold injecting electrodes. From the channel-length dependence of the transistor resistance in the conducting ON-state, we determine the field-effect mobility and the parasitic series resistance. The extracted parasitic resistance, typically in the M⍀ range, depends on the applied gate voltage, and we find experimentally that the parasitic resistance decreases with increasing field-effect mobility. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1581389͔The interest in organic thin-film transistors ͑TFTs͒ has grown rapidly due to envisaged applications, such as integrated circuits 1 and active-matrix displays. 2 The switching speed of organic integrated circuits can be estimated from the performance of the individual transistors and is roughly proportional to ϳ FE /L 2 , 3 where L is the channel length of the transistor, and FE is the field-effect mobility. To reach higher switching speeds, the search for higher mobility materials is therefore important, but it is also of great interest to downsize the transistor geometries. In this work, the scaling behavior of the transfer characteristics with transistor channel length is investigated for a variety of solutionprocessable organic TFTs.In the experiments, we use heavily doped Si wafers as the gate electrode, with a 200-nm-thick layer of thermally oxidized SiO 2 as the gate-insulating layer. Using conventional lithography, gold source and drain contacts 100 nm thick are defined, with channel widths ranging from 1 mm to 1 cm and channel lengths between 0.75 and 40 m. The structures typically have an underetch of 0.5 m, which we neglect in the following analysis. A 10-nm layer of titanium acts as an adhesion layer for the gold on the SiO 2 . The SiO 2 layer is treated with the primer hexamethyldisilazane to make the surface hydrophobic. No special care is taken to clean the gold surface prior to deposition of the semiconductor. Poly͑2,5-thienylene vinylene͒ ͑PTV͒ films as semiconductor layer are deposited using a precursor-route process. 3 We systematically varied the processing conditions for the conversion from precursor to PTV, and we determined the average degree of conversion using the method described by Fuchigami et al. 4 This enabled us to systematically study PTV transistors at various degrees of conversion ranging from 60% to 100%, and consequently over a range of field-effect mobilities, between 10 Ϫ4 and 10 Ϫ3 cm 2 /V s. Poly͑3-hexyl thiophene͒ ͑P3HT͒ is spin-coated from a 1 wt % chloroform solution. Films of poly͓͑2-methoxy-5-(3Ј,7Ј-dimethyloctyloxy͔͒-p-phenylene vinylene͒ (OC 1 C 10 -PPV) and poly͓͑2,5-di-(3Ј,7Ј-dimethyloctyloxy͔͒-p-phenylene vinylene͒ (OC 10 C 10 -PPV), are spun from a 0.5 wt % toluene solution. Pentacene thin films are deposited using a precursor-route process. 3 The measurements are performed on freshly...