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 PMMA 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 layer. 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. Copyright © 2009 John Wiley & Sons, Ltd.