Surface polarization in a poly(4-vinyl phenol) (PVP) dielectric induced by water molecules has been qualitatively investigated in pentacene thin-film transistors. The magnitudes of drain currents from devices with PVP dielectrics subject to specific surface treatments increased with humidity, whereas the opposite responses were observed from device with SiO2 dielectrics. The increase in drain current is attributed to the accumulation of extra charge carriers induced by the surface polarization in addition to that by the vertical electric field. Such polarization effects should be carefully considered in characterizing organic and polymer thin-film transistors, particularly those with polymeric gate insulators.

The electrical characteristics of bottom-contact organic field-effect transistors fabricated with the air-stable n-type semiconductor N,N′-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN2) are described. The mobility, threshold voltage, subthreshold swing, and Ion∕Ioff ratio(VDS=40V, VG=0∼40V) are 0.14cm2∕Vs, 1.6V, 2.0V/decade, and 1.2×103, respectively. The effect of electrode/dielectric surface treatment on these devices is also examined, with a combination of 1-octadecanethiol and hexamethyldisilazane. Organic complementary five-stage ring oscillators were fabricated using pentacene and PDI-8CN2, and operated at an oscillation frequency of 34kHz and a propagation delay per stage of 3μs.

Printed electronic circuits have been explored for low-cost, large-area applications, such as displays and radio frequency identification tags, where the promise of inexpensive solutionbased fabrication techniques is more crucial than the fast circuit speeds associated with conventional inorganic semiconductors. [1][2][3][4][5][6][7][8] In order for such low-cost, portable devices to become a reality, high-mobility, air-stable, n-channel organic field-effect transistors (OFETs) are required to enable the fabrication of organic complementary metal oxide semiconductor (CMOS) circuits that would operate at sufficient speeds and with low power dissipation. Additionally, the semiconductors must be solution processable to be compatible with the inexpensive fabrication techniques envisioned for printed electronics. Whereas most examples of printed organic semiconductors are conjugated p-type polymers, solution-processed OFETs with small molecules are far less common. [9,10] Previously, the small molecule semiconductor N,N′-bis(n-octyl)-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicar-boximide) (PDI-8CN 2 ) was used to fabricate promising vapordeposited n-channel OFETs with excellent electrical performance and remarkable environmental stability. [11,12] Because PDI-8CN 2 is soluble in common solvents such as chloroform, toluene, and dichlorobenzene, an intriguing question of whether it could be used for fabricating complex complementary organic circuits using solution-based processing techniques is raised. We report here the first fabrication of highperformance n-channel organic transistors and their complementary circuits from a PDI-8CN 2 solution with a micro-injector patterning technique. This work advances the pioneering results of Katz et al., [13] who fabricated a simple organic complementary inverter with a shadow-masked top-contact geometry. Unfortunately, such simple fabrication methods are not scalable for shrinking channel lengths to technologically useful sizes or for increasing the circuit complexity beyond inverter structures. These last two points represent the crossing of major technical hurdles in the development of organic complementary circuit technology. For the present OFET device fabrication, the organic semiconductor solutions were patterned in a nitrogen atmosphere using an Intracel Picospritzer, a pneumatically actuated micro-injector where droplet size is controlled by gas pressure and jetting time. The OFET gate dielectric and gold source/ drain electrode surfaces were treated with self-assembled monolayers (SAMs) to improve the surface energy match with the organic semiconductors and to produce approximately hemispherical solution droplets. Solvent selection proved crucial to the formation of uniform semiconductor films-for example, low-boiling solvents, such as chloroform, leave residue on the micropipette tip, adversely affecting the deposition process and the resultant film morphology. However, high-boiling solvents, such as 1,2-dichlorobenzene (bp 174°C) do not adversely affect the solution de...

The field effect in pentacene thin-film transistors was studied using bottom-contact devices with channel lengths below 10nm. To suppress spreading current in these devices, which have a small channel width-to-length (W-L) ratio, we employed a pair of guarding electrodes as close as 20nm to the two sides of the channel. The responses of these nanometer scale transistors exhibit good gate modulation. Mobilities of 0.046cm2∕Vs and on/off ratios of 97 were achieved in sub-10-nm transistors. We find that the device response is strongly influenced by the nature of the metal-semiconductor contact.

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