Stacked pentacene layer organic thin-film transistors with improved characteristics

Using two layers of pentacene deposited at different substrate temperatures as the active material, we have fabricated photolithographically defined organic thin-film transistors (OTFT's) with improved field-effect mobility and subthreshold slope. These devices use photolithographically defined gold source and drain electrodes and octadecyltrichlorosilane-treated silicon dioxide gate dielectric. The devices have field-effect mobility as large as 1.5 cm²/V-s, on/off current ratio larger than 10⁸, near zero threshold voltage, and subthreshold slope less than 1.6 V per decade. To our knowledge, this is the largest field-effect mobility and smallest subthreshold slope yet reported for any organic transistor, and the first time both of these important characteristics have been obtained for a single device.