Transistor sexithiophene

Francis Gamier [3, and references given therein] fabricated the first transistor using molecules of sexithiophene. The transistor could be twisted, bent or rolled without degrading its characteristics. Computers fabricated using these devices will work at less than one thousandth of the speed of those made with amorphous Si transistors. They would be useful in video displays and liquid-crystal displays. In active matrix displays, each pixel is controlled individually by a thin film transistor. A 50 cm full color display contains more than two million pixels. Organic transistors, considerably cheaper than the amorphous Si transistors being used at present, will be a boon to the manufacturers. 

Chwang, A. B., and Frisbie, C. D., Field effect transport measnrements on single grains of sexithiophene Role of the contacts, J. Phys. Chem. B, 104, 12202, 2000. Zaumseil, J., Baldwin, K. W., and Rogers, J. A., Contact resistance in organic transistors that use source and drain electrodes formed by soft contact lamination, J. Appl. Phys., 93, 6117, 2003. 

Horowitz, G. et al.. Field-effect transistor made with a sexithiophene single crystal,... 

Another LB multilayer thin film is produced from mixed monolayers containing PHT and 3-octadecanoylpyrrole [426,427]. PHT/arachidic acid and quinquithiophene/arachidic acid LB films are used in thin film field-effect transistors (cf. Sect. 6.6) [428]. Some excellent LB films contain sexithiophene and 9,10-diphenylanthracene with arachidic acid [383]. Molecular structure devices can be composed of LB films of PHT and poly(pyrrole) [429]. Another type of conducting LB film contains PT salts [431], polyion complexes of acid-functionalized PT, and sulfonated poly(aniline) [431] or polyfheptadecyl 3-thienylacetate) [365]. 

G. Horowitz, F. Gamier, A. Yassar, R. Hajlaoui and F. Kouki, Field-effect transistor made with a sexithiophene single-crystal, Adv. Mater., 1996,8, 52. 

Another important research field aims at controlling the molecular and structural ordering of semiconducting PT in view of improving its charge transport properties. A major advance in this direction has been realized in 1987 at CNRS, Thiais, with the synthesis of sexithiophene (6T), the linear hexamer of thiophene, and its use to fabricate an organic transistor whose performances are close to those of silicon-based devices. The spectacular increase of the carrier mobility in polycrystalline... 

Alkoxysilane SAMs deposited on oxidized silicon as ultrathin dielectrics in thin film transistors were first explored by the group of Vuillaume in both inorganic [53] and organic devices [54]. The SAM consisted of vinyl-terminated molecules that were subsequently oxidized to obtain a carboxyl-terminated monolayer. In the organic case, the authors combined electron beam lithography and lift-off of both the source drain electrodes and semiconductor layer. The source drain distance was as low as 30 nm. The device functioned at low voltage (2 V), but the overall performance remained modest, partly because of the nature of the semiconductor (sexithiophene). 

Device design has been further improved to reduce the costs for the fabrication of such all-organic transistors. Another development has overcome the disadvantage that transistors based on a-sexithiophene operate only as p-channel devices, that is, they only support the flow of holes and not of electrons. n organic FET that functions as either an n-channel or a p-channel device, depending on the gate bias, needs two active semiconducting materials. This can be achieved with a thin (<40-nm) layer of a-sexithiophene (as hole conductor) topped with a second layer composed of CgQ (as electron conductor). 

How much do the results we have obtained here tell us about the fundamental limits to the mobilities of carriers in devices fabricated with polymer that is very much better ordered than the polyacetylene that we have used here There are recent reports of very much improved mobilities for devices based on sexithiophene (the six repeat unit oligomer of polythiophene), with a value of 0.4 cm /Vsec now reported [73], and there is now considerable interest in the development of polymer FETs as large area thin film transistors, with interest in polythiophene derivatives [74] and in poly(arylenevinylenes) such as poly(2,5-thienylene vinylene) [75]. We can see from the optical characterisations of the MIS devices that the surface layer of polyacetylene formed on SiC>2 is very much more disordered than the bulk material, but we have not made FET devices with the polymer insulator layers which give better ordered structures as characterised optically. 

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