Contact effects in organic thin film transistors with printed electrodes

The influence of contact effects on the performance of pentacene thin film transistors with printed electrodes was investigated. The electrodes of the transistor were realized by a combination of microcontact printing and selective dewetting/wetting. Printing of silane based self-assembled monolayers on glass or silicon substrates allows for the modulation of the surface energy, so that polymers or resists can be selectively deposited in the hydrophilic regions of the substrate, whereas the hydrophobic regions stay uncoated. A poly methyl methacrylate (PMMA) resist was selectively deposited in the hydrophilic regions. The resists structures were used as a template to pattern electrodes of pentacene thin film transistors by a lift-off process. The transistors exhibit charge carrier mobilities of 0.2 cm2/V s, low threshold voltages, and high on/off ratios of 106. The pentacene transistors with printed drain and source electrodes were compared to devices patterned by optical lithography. In particular the influence of the drain and source contacts on the charge carrier mobility of the devices will be discussed. A simple model will be presented which takes the influence of contact effects into account when describing the electrical behavior of the transistors.