Theory and modelling of organic field effect transistors

In organic FET ́s (OFET) the active layer is an organic material. Until now measured current characteristics have been analyzed by using the most simple equation for the current. But the design of the OFET is not common in electronics. As demonstrated by our 2D simulations of analogous silicon devices this design leads to several peculiarities. We developed analytical models which incorporate these peculiarities and reproduce the simulated current characteristics with less than 3 to 5% error. As first applications we fitted published current characteristics of OFET ́s and determined in this way material parameters. Zero field mobility μ0 is low and indicate hopping transport. Large flat band voltages must origin from oxide/interface charges. Satisfactory fits are possible only by assuming velocity saturation unknown till now for hopping systems. The ratio vs/μ0 ~ 1.5⋅104V/cm can be explained theoretically.