Effect of electrode thickness on bottom-contact pentacene thin-film transistors

The usual way of fabricating bottom-contact pentacene field effect transistors (FETs) is to vacuum-evaporate pentacene molecules onto a substrate with patterned electrodes. We observed that the heights of the source and the drain electrodes affected the drain current of a pentacene FET made in this way. Atomic force microscopy measurements of the patterned substrate coated with pentacene revealed a region in the channel where pentacene (lid not adsorb along the electrodes edge. This pentacene-denuded zone was caused by the sticking coefficient of pentacene molecules to the side wall of the metal electrode being higher than that of pentacene molecules to other nucleation sites on the Si-oxide channel. The denuded zone was eventually filled with pentacene by prolonged deposition, but when and how it was filled depended on the height of the electrode. Our study suggests that different heights of the electrodes affect the drain current via the formation of a pentacene-denuded zone.