We report on parasitic contact effects in organic thin film transistors (OTFTs) fabricated with pentacene films. The influence on the OTFT performance of the source and drain contact metal and the device design was investigated. Top contact (TC) and bottom contact (BC) gated transmission line model (gated-TLM) test structures were used to extract the combined parasitic contact resistance as a function of gate voltage swing and drain-source voltage for OTFTs with gold source and drain contacts. For comparison BC test structures with palladium contacts were studied. Differences in the bias dependence of the contact resistance for TC and BC OTFTs indicate that charge injection and device performance are strongly affected by the device design and processing. The results from this investigation show that TC and BC device performances may be contact limited for high mobility OTFTs with channel lengths less than 10μm.

Analysis of carrier transport in quaterrylene thin film transistors formed by ultraslow vacuum deposition J. Appl. Phys.

We have fabricated organic thin-film transistors (TFT's) using the small-molecule polycyclic aromatic hydrocarbon pentacene as the active material. Devices were fabricated on glass substrates using low-temperature ion-beam deposited silicon dioxide as the gate dielectric, ion-beam deposited palladium for the source and drain contacts, and vacuum-evaporated pentacene to form the active layer. Excellent electrical characteristics were obtained, including carrier mobility as large as 0.6 cm 2 /V-s, on/off current ratio as large as 10 8 , and subthreshold slope as low as 0.7 V/dec, all record values for organic transistors fabricated on nonsingle-crystal substrates. Jonathan A. Nichols received the B.A. degree in physics from Edinboro University, Edinboro, PA, and the B.S. degree in materials science and engineering from the Pennsylvania State University, University Park, in 1998, where he is currently pursuing the M.S. degree in materials engineering at the Center for Thin Film Devices. His research focuses on the processing and material characterization of organic thin-film transistors.

Scanning Kelvin probe microscopy (SKPM) has been used to simultaneously obtain high-resolution topographical and potential images of pentacene organic thin-film transistors (OTFTs) during device operation. SKPM images of OTFTs show large potential drops at the source with the magnitude dependent on contact metallurgy and relatively small potential drops at grain boundaries in polycrystalline pentacene films.

We have fabricated and characterized analog and digital circuits using organic thin-film transistors on polyester film substrates. These are the first reported dynamic results for organic circuits fabricated on polyester substrates. The high-performance pentacene transistors yield circuits with the highest reported clock frequencies for organic circuits.