Organic thin-film transistors with polymeric gate insulators

Copper phthalocyanine (CuPc) thin-film transistors (TFTs) have been fabricated using spin-coated polymeric gate insulators, including polymethyl methacrylate (PMMA) and a novel poly(methylmethacrylate-co-glycidylmethacrylate) (P(MMA-co-GMA)). These devices behaved fairly well and showed satisfactory p-type electrical characteristics. The transistor with P(MMA-co-GMA) gate insulator showed higher field-effect mobility, μFET = 1.22 × 10−2 cm2/V s, larger on/off current ratio, Ion/Ioff = 7 × 103 and lower threshold voltage, VT = −8 V, compared with the transistor with PMMA gate insulator (μFET = 5.89 × 10−3 cm2/V s, Ion/Ioff = 2 × 103 and VT = −15 V). The higher mobility of CuPc on P(MMA-co-GMA) was attributed to better ordering and enhanced crystallinity within the CuPc film and the better CuPc/P(MMA-co-GMA) interface, as observed by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) measurements. The correlation between the structural properties and the device performance of CuPc films grown on different polymeric gate insulators is discussed.