Influence of H2O and O2 on threshold voltage shift in organic thin-film transistors: Deprotonation of SiOH on SiO2 gate-insulator surface

The influence of H2O and O2 on the transistor characteristics in p- and n-type organic thin-film transistors (OTFTs) fabricated on the SiO2 gate insulator was investigated. In both p- and n-type OTFTs, the threshold voltage (Vth) shifted drastically to positive direction after exposure to ambient air and dry air, although the field-effect mobilities in saturation regime were almost unchanged before and after the Vth shift. The Vth shifts to the positive direction indicate that negative charges are generated on the SiO2 gate-insulator surface by exposure to ambient air and dry air. The influence of SiO− on the gate-insulator surface and deprotonation processes of SiOH caused by H2O and O2 were discussed as the origin of the significantly positive Vth shift.