Ion implantation effects on organic thin film transistors

One of the open issues in organic electronics is the long-term stability of devices based on organic materials, as oxidation is believed to be a major reason for early device failure. The focus of our research is to investigate the effects of low energy ion implantation in the reduction and control of the degradation of organic devices due to the exposure to atmosphere (i.e. oxygen and water). We have studied the effects of N and Ne irradiation on pentacene organic thin film (50nm thick) transistors (OTFTs). Ion implantation induces strong molecular structure modifications that affect the organic active layer, but we have observed that a controlled damage depth distribution preserves the functionality of the device and its major transport parameters, i.e. carrier mobility and threshold voltage. The electrical properties of the pentacene layer and of the OTFT have been investigated by means of current-voltage and photocurrent spectroscopy analyses. We have characterized the structural modification induced by ion implantation and we have monitored the effectiveness of this process in stabilizing the device carrier mobility and threshold voltage over a long time (over 2000 hours), proving how ion implantation can be safely carried out on fully operational OTFTs. In particular, we have assessed by depth resolved X-ray Photoemission Spectroscopy analyses that, by selectively implanting with ions that can react with the hydrocarbon matrix (e.g. N+), it is possible to locally modify the charge distribution within the organic layer.