Tuning of threshold voltage in organic field-effect transistors with hydrophobic gate dielectric using monoenergetic low-energy electron beams and triode corona

We report organic field-effect transistors (OFETs) with the hydrophobic gate dielectric exposed to an electron beam before semiconductor deposition, shifting the threshold voltage toward positive gate bias for a p-channel semiconductor. A 1 mu m Cytop film was irradiated with defined doses of electron beams with different energies. The charges/polarizations embedded in the dielectric by the irradiation have effective charge densities of similar to 10(-8) C/cm(2). OFETs were completed using 5,5'-bis(4-hexylphenyl)-2,2'-bithiophene as the semiconductor, and showed corresponding shifts in Vth. Other OFETs were made where the gate dielectric was treated with a corona discharge. Both types of devices showed similar shifts in Vth and transfer characteristics. There is no change in mobility of the charge carriers after either charging process. The charges do not contribute to the gate capacitance but induce changes in the onset of capacitance increase caused by accumulation of mobile channel charge during capacitance-voltage experiments in two-terminal metal-insulator-semiconductor-metal configurations. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3222854]