Investigation of electron trapping behavior in n-channel organic thin-film transistors with ultrathin polymer passivation on SiO_2 gate insulator

摘要

Electron trapping behavior at the interface between N,N'-ditridecyl-3,4,9,10-perylene tetracarboxylicdiimide (PTCDI-C13) film and thermal SiO_2was investigated by utilizing ultrathin poly(methyl methacrylate) (PMMA) gate passivation layers. From the capacitance-voltage analysis for the PTCDI-C13/PMMA/SiO_2interface, it is found that the electron tunneling appeared with PMMA thinner than 0.8 nm, and that the thickness of the gate passivation layer should be at least 1 nm for preventing injection-type hysteresis in the capacitance-voltage curve. The effective electron mobility of organic thin-filmtransistors (OTFTs) based on PTCDI-C13 with SiO_2 gate insulator was increased by suppressing shallow-level interface traps on SiO_2 with the PMMA layer, which can be partially accounted for by the multipletrap and release model. In this work, the thickness and the density of the PMMA layers were preciselycontrolled with a simple spin-coating process. Even 1.3-nm thick PMMA layer caused the improvementsof the electron mobility and the air stability of the n-channel conduction.