Modeling the Impact of a Non-Ohmic Contact on the Delay of Complementary OTFT Inverters

To be commercially successful, printed organic electronics need to include minimal signal processing abilities. Rudimentary intelligence relies on sufficiently fast digital circuits based on thin-film transistors (TFTs). A key material parameter for high-frequency operation is the charge carrier mobility. However, organic semiconductors frequently already surpass the mobility of amorphous silicon. Thus, development efforts recently shifted towards the reduction of the contact resistance to further increase the operating frequency. Contact resistance values for organic TFTs are orders of magnitude higher than for silicon technologies and critically limit the TFT current drive. Probably even more important, the charge injection across an organic metal-to-semiconductor interface shows a non-ohmic bias dependence. In the present work, we estimate the deteriorative effect of non-ohmic contacts on the delay of complementary inverters at a given current drive. Moreover, we advocate the use of table circuit models in the absence of physical compact models and related extraction strategies for bias-dependent contact resistances.