OFETs contacts

CuPc thin films, and the enhanced physical connection between source-drain electrodes and semiconductor channel associated with the PMMA polymer layer, the OFET performance of this bottom-contact device was significantly improved with leakage current being reduced by roughly one order of magnitude and on-state current enhanced by almost one order of magnitude. The hole mobility of this bottom-contact OFET device reached 0.01 cm2 V-1 s 1, which is comparable with that of top-contact device but much higher than that of normal bottom-contact device without polymer layer [45],... 

Figure 2 Scheme of a bottom-contact OFET illustration of the current research topics including the stmcture and morphology of organic semiconductor films as well as charge carrier transport and injection mechanism, which are the subject of this book. 

For the top-contacted OFETs, highly p-doped silicon substrates with 100 nm thermally grown Si02 were used. For contacting the structure in situ, it was... 

Figure 5.11 shows the output characteristics of the top contacted OFET structure using gold source-drain contacts. The drain current is plotted as function of the drain voltage Kjjs with reversibly sweeping the applied gate voltage Vq from -12 V to -4 V. 

Figure 5.11 Output characteristics of the top contact OFET with gold source-drain contacts. Good satnration properties are observed for aU gate voltages. Also note the forward/hackward hysteresis.

Figure 5.12 Transfer characteristics of the top contact OFET with DCNDBQT oligomer and gold source-drain contacts (a) Enlarged section of transfer characteristic (h) complete characteristic (note the different scales).

Top contact OFETs (Fignre 2.4.7a) generally exhibit the lowest contact resistances. This is likely becanse of the increased metal-semicondnctor contact area in this configuration. A major contribution to contact resistance in the top contact configuration is access resistance (see Figure 2.4.8a). Access resistance resnlts from the requirement that charge carriers must travel from the source contact on top of the film down to the accnmnlation layer (the channel) at the semicondnctor-insnlator interface and then back np to the drain contact to be extracted. 

In order to minimize access resistance, the thickness of the organic semiconductor layer should not be too large. However, some researchers have proposed that access resistance is less than might be expected for top contact OFETs becanse the contact metal penetrates the film down to the accnmnlation layer (perhaps dne to large peak-to-valley ronghness of the semicondnctor film or the natnre of the metal deposition process) [11]. This scenario is shown in Fignre 2.4.8(b). 

Fig. 5.3. A schematic illustration of the molecular packing in (a) top and (b) bottom contact OFET devices. Small molecules deposited on metal contacts tend to lie flat, and do not have a contiguous grain structure where the molecules are standing vertically at the center of the channel.

Figure8.13 Field-effect mobility of holes and (a) 130°Cand(b) 160°C. t = 5[i.m, electrons in a 1 1 (wt%) P3HT [60]PCBM blend V/= 10 mm for both OFETs. (Reproduced from ambipolar bottom-gate, bottom-contact OFET Ref. [77] with permission of john Wiley Sons, as a function of time, while being annealed at Inc.)...

Bottom-gate, bottom-contact OFET devices were fabricated from pBTTT polymer solutions and hole... 

Figure 17.8 Transfer characteristics of bottom-gate, bottom-contact OFET device with (a) P3FIT and (b) pBTTT semiconductor on continuous exposure to ambient, unfiltered air (c) pBTTT on continuous exposure to filtered, low humidity ( 4 % RFi) air. Reprinted with permission from M. Fieeney, C. Bailey, K. Cenevicius, M. Shkunov, D. Sparrowe, S. Tierney and i. McCulloch, Stable polythiophene semiconductors incorporating thieno[2,3-b]thiophene. J. Am. Chem. Soc., 127, 1078-1079 (2005). Copyright 2005 American Chemical Society...

As a low-cost alternative to traditional inorganic semiconductors based transistors, organic field effect transistors are ideally positioned for applications such as radio frequency ID tags, sensors, and smart banknotes [36-40]. An archetypical structure of a bottom-gate top-contact OFET is shown in Scheme 3.7a. Other device architectures have also been employed depending on the relative... 

Scheme 3.7 a) a t) ical structure of bottom-gate top-contact OFET b) bottom-gate top-contact c) bottom-gate bottom-contact d) top-gate bottom-contact e) top-gate top-contact. 

Fig. 13 Schematic of the bottom-gate oiganic field-effect transistors (OFETs) with (a) top contact and (b) bottom contact structures. Schematic diagram of a (c) top-gate/bottom contact OFETs using a standard TFT device structures and (d) top-gate/top contact is also shovm. (Reproduced...

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