Ultrathin polymer gate buffer layer for air-stable, low-voltage, n-channel organic thin-film transistors

An ultrathin poly(methyl methacrylate) (PMMA) buffer layer was developed to improve the performance of n-channel organic thin-film transistors (OTFTs). The 8 nm-thick PMMA film, prepared by spin-coating, provided a very smooth surface and a uniform coverage on SiO₂ surface reproducibly, which was confirmed by X-ray reflectivity (XR) measurement. Then, we fabricated N,N'-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C13) thin-film transistors with and without this 8 nm-thick PMM₂ A insulating layer on SiO₂ gate insulators and achieved one-order increase of field-effect mobility (up to 0.11 cm²/(Vs) in a vacuum), one-half decrease of threshold voltage, and reduction of current hysteresis with the PMMA layer₂. Only TFTs with the PMMA layer displayed n-channel operation in air and showed field-effect mobility of 0.10 cm²/(Vs). We consider that electrical characteristics of n-channel OTFTs were considerably improved because the ultrathin PMMA film could effectively passivate the SiO₂ insulator surface and decrease interfacial electron traps. This result suggests the importance of the ultrathin PMMA layer for controlling the interfacial state at the semiconductor/insulator interface and the device characteristics of OTFTs.