Process control of threshold voltage in organic FETs

We report a technique for systematically modifying the threshold voltage of pentacene organic FETs at the process level. Threshold voltage control is critical to practical circuit design using OFETs, since it ultimately determines circuit functionality and yield. This work shows that oxygen plasma and UV-ozone treatments of an organic polymer gate dielectric, parylene, introduce traps at the semiconductor-dielectric interface. We model the effects of trap-introduced charges as both fixed charges that shift the threshold voltage and mobile charges that increase parasitic bulk conductivity. I-V and C-V characterization confirm that threshold voltage can be varied from - 27V to +26V by exposure to UV-ozone and from -17V to +116V by exposure to oxygen plasma. Optical measurements confirm the presence of a trap level at 420nm (3.0eV) in response to the treatment.