On the degradation of organic field-effect transistors

Degradation experiments with organic thin film transistors (OTFT) made of the p-conducting organic semiconductor pentacene revealed a distinct dependence of the electrical transistor parameters to the ambient conditions. A sample that was kept unprotected in dark ambient air conditions was found to be still operating after 9 months of degradation. The on-current was reduced by one order of magnitude per quarter year and the threshold voltage shifted to negative values. To study the influence of the respective gases of the atmosphere, an OTFT was characterized in vacuum conditions and exposed to the distinct gases. The exposure of the unprotected organic film to oxygen resulted in a decreasing on-current, on-off ratio and a positive shift of the threshold voltage, due to scattering centers formed by the reaction of oxygen with the pentacene. Nitrogen caused a decrease of the on-current with reversible tendency when the vacuum conditions were re-established.