Fast organic thin-film transistor circuits

We have fabricated organic thin-film transistors and integrated circuits using pentacene as the active material. Devices were fabricated on glass substrates using low-temperature ion-beam sputtered silicon dioxide as the gate dielectric and a double-layer photoresist process to isolate devices. These transistors have carrier mobility near 0.5 cm²/V-s and on/off current ratio larger than 10/sup 7/. Using a level-shifting design that allows circuits to operate over a wide range of threshold voltages, we have fabricated ring oscillators with propagation delay below 75 μs per stage, limited by the level-shifting circuitry. When driven directly, inverters without level shifting show submicrosecond rise and fall time constants.