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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 highperformance organic transistors on flexible, transparent plastic substrates requiring low operating voltages.
Introduction For more than a decade now, organic thin-film transistors (OTFTs) based on conjugated polymers, oligomers, or other molecules have been envisioned as a viable alternative to more traditional, mainstream thin-film transistors (TFTs) based on inorganic materials. Because of the relatively low mobility of the organic semiconductor layers, OTFTs cannot rival the performance of field-effect transistors based on single-crystalline inorganic semiconductors, such as Si and Ge, which have charge carrier mobilities (mu) about three orders of magnitude higher [1]. Consequently, OTFTs are not suitable for use in applications requiring very high switching speeds. However, the processing characteristics and demonstrated performance of OTFTs suggest that they can be competitive for existing or novel thin-film-transistor applications requiring large-area coverage, structural flexibility, low-temperature processing, and, especially, low cost. Such applications include switching devices for active-matrix flat-panel displays (AMFPDs) based on either liquid crystal pixels (AMLCDs) [2] or organic light-emitting diodes (AMOLEDDs) [3, 4]. At present, hydrogenated amorphous silicon (a-Si:H) is the most commonly used active layer in TFT backplanes of AMLCDs. The higher performance of polycrystalline silicon TFTs is usually required for well-performing AMOLEDDs, but this field is still in the development stage; improvements in the efficiency of both the OLEDs and the TFTs could change this requirement. OTFTs could also be used in active-matrix backplanes for "electronic paper" displays [5] based on pixels comprising either electrophoretic ink-containing microcapsules [6] or "twisting balls" [7]. Other applications of OTFTs include low-end smart cards and electronic identification tags.
There are at least four ways in which a new, exploratory technology such as OTFTs can compete with or supplement a widely used, entrenched technology such as (a-Si:H) TFTs, for which...