Band OFETs

But, it is substantially better than the tens of kilohertz that classic amorphous silicon or OFETs can achieve. It is also in frequency ranges of interest for many mobile communication systems and radar detection bands and, therefore, would provide sufficient capability for a range of RF opportunities. 

In order to co-polymerize the IC unit, Suzuki and Stille polymerizations have been used. First, Blouin et al. [94] were able to obtain polyindolo[3,2-fr]-carbazole derivatives with bithiophene or biEDOT as co-monomers. Unfortunately, these studies demonstrated a relatively low oxidation potential for these polymers (especially for P35 and P37), limiting their applications in OFETs and PCs. However, for doped state applications, these polymers may exhibit interesting properties [35]. For instance, when copolymerized with bithiophene, the resulting copolymer shows a good electrical conductivity (as high as 0.7 Scm 1) but a low Seebeck coefficient of 4.3 iV K 1 [35]. Finally, the UV-Vis absorption maxima are similar for poly(2,8-indolocarbazole-a/f-bithiophene) and poly(2,8-indolocarbazole-a/f-bis(3,4-ethylenedioxythiophene)). A broad absorption band is centered at 430 nm whereas, for the 3- and 9-substituted copolymers, the broad band is centered around 490-500 nm [94],... 

OFETs are the basis of all logie deviees that are required to eontrol, for example, the intensity of a display pixel (the so ealled all organic display) or the realisation of a radio frequeney identifieation (RFID) tag. Sinee for the latter applieations only limited frequeney bands are available (essentially 13.56 MHz or 900 MHz) this plaees rather strong eonstraints on the required switehing properties of the OFETs. 

As soon as Ep - Ejjomo becomes smaller than k T, the OFET s conductance increases by several orders of magnitude due to the thermal excitation of the carriers from the localized states into the HOMO band. As a result, a conduction channel is formed at the interface between the semiconductor and the gate dielectric. Overall device operation depends, to a large extent, on the energetics of the semiconductor bands and metal contacts, and therefore studies of the electronic structure of molecular interfaces are important [58],... 

FIGURE 2.1.9 The schematic diagram of the energy distribution of localized electronic states in the energy gap between the HOMO and LUMO bands in the rubrene single-crystal OFETs. (From Podzorov, V. et al., Phys. Rev. Lett., 93, 086602, 2004.)... 

While it is simpler from a fabrication standpoint to deposit the same contact material for both the source and drain contacts (symmetric contacts), one may also consider choosing two different materials for each contact (asymmetric contacts). Based on energy band line-up considerations with the semiconductor HOMO and LUMO levels, depositing two different contact materials at either end of the transistor channel may facilitate more efficient hole and electron injection, respectively. At this point, it is unclear whether separately engineering distinct contacts for hole/elec-tron injection in ambipolar OFETs will prevail over opting for symmetric contacts. However, there will certainly be more reports on this exciting OFET subclass in the next few years. 

The doped state of PEDOT is almost transparent as the polaron bands absorb in the infrared (IR) region. The de-doped form of PEDOT is dark blue with an absorption maximum located slightly above 600 nm. As PEDOT is highly conducting in pristine state, it caimot be used as channel material in depletion mode OFETs. Instead, the good ion mobility of PEDOTrPSS and other PEDOT analogues makes this material ideal for... 

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