One important technical hurdle that has to be overcome for using organic transistors in radio-frequency identification tags is for these devices to operate at rf frequencies (typically 13.56MHz) in the front end. It was long thought that organic transistors are too slow for this. In this letter we show that organic transistor based full-wave rectifier circuits utilizing pentacene, a p-channel organic semiconductor, can operate at this frequency with a useful efficiency. In order to achieve such high-frequency operation, we make use of the nonquasistatic state of the transistors.

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.

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...

Thin films based on the tolyl‐substituted oligothiophenes 5,5′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′‐terthiophene (1), 5,5′′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′:5′′,2′′′‐quaterthiophene (2) and 5,5′′′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′‐quinqethiophene (3) exhibit hole‐transport behavior in a thin‐film transistor (TFT) configuration, with reasonable mobilities and high current on/off (Ion/Ioff) ratios. Powder X‐ray diffraction (PXRD) reveals that these films, grown by vacuum deposition onto the thermally grown silicon oxide surface of a TFT, are highly crystalline, a characteristic that can be attributed to the general tendency of phenyl groups to promote crystallinity. Atomic force microscopy (AFM) reveals that the films grow layer by layer to form large domains, with some basal domain areas approaching 1000 μm2. The PXRD and AFM data are consistent with an “end‐on” orientation of the molecules on the oxide substrate. Variable‐temperature current–voltage (I–V) measurements identified the activation regime for hole transport and revealed shallow level traps in thin films of 1 and 2, and both shallow and deep level traps in thin films of 3. The activation energies for thin films of 1, 2, and 3 were similar, with values of Ea = 121, 100, and 109 meV, respectively. The corresponding trap densities were Ntrap/Nv = 0.012, 0.023, and 0.094, where Ntrap is the number of trap states and Nv is the number of conduction states. The hole mobilities for the three compounds were similar (μ ≃ 0.03 cm2 V–1 s–1), and the Ion/Ioff ratios were comparable with the highest values reported for organic TFTs, with films of 2 approaching Ion/Ioff = 109 at room temperature.

3) were grown by vacuum deposition on thermally grown SiO 2 substrates and characterized in a thin film transistor (TFT) configuration. Atomic force microscopy and specular (θ-2θ) X-ray diffraction (XRD) revealed films with small, crystalline grains, in which the oligothiophenes were oriented "end-on" with respect to the SiO 2 substrate. Interplanar spacing increased (1 ) 28.0 Å, 2 ) 29.5 Å, 3 ) 37.7 Å), consistent with increasing alkyl tail length. Grazing incidence X-ray diffraction (GIXD) of the films (ca. 350 Å thick) revealed nearly equivalent in-plane unit-cell areas (1 ) 44.1 Å 2 , 2 ) 44.4 Å 2 , 3 ) 43.8 Å 2 ). The films functioned as p-channel semiconductors in a TFT configuration, exhibiting nearly equivalent hole mobilities (µ ≈ 0.05 ( 0.01, 0.04 ( 0.01, 0.06 ( 0.01 cm 2 /Vs for 1, 2, and 3, respectively). Variable-temperature measurements demonstrated that the activation energy of the mobility for thin films of 3 was ∼55 meV. The increasing alkyl chain length does not appear to improve molecular ordering; however, the addition of a phenyl end-substituent appears to greatly improve the on-to-off ratio in TFTs.